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Paisley Grammar School Physics Department

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Study Guides Summary Notes Problem Sheets

Homework Sheets

UNIT 3 Waves and Radiation

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Waves & Radiation Working at Home

TO THE PUPIL Each day you have physics at school, you should set aside time for work at home. By this stage you should be accepting more responsibility for your own learning and should undertake the following tasks on a regular basis:

• Tackle the supplied homework sheets as each section of work is completed in class.

• Check your own progress in the homework sheets. Discuss any difficulties that arise with your class teacher.

• Complete any Large homework tasks that your teacher will issue from time to time and hand them in on the

due date for marking.

• Revise the work you have covered in class activities by referring to your classwork jotters.

• Complete the supplied summary notes as the coursework allows you to, then use the summary notes to help you in your revision of the course content.

• Make your own short notes to cover each learning outcome in the supplied study guides.

TO THE PARENT Your co-operation would be appreciated in ensuring that pupils are encouraged to complete homework. It would be helpful if you could talk over the work given for homework and sign the homework record sheet on this page after they have completed each exercise. The physics department hopes that this record of your child's achievement will be of interest to you, and we would welcome any comments on this or other areas related to the work of the department. Please sign here to confirm that you have seen the homework record sheet: HOMEWORK RECORD SHEET

HOMEWORK SECTION OF WORK MARK CHECK PARENTAL SIGNATURE 3.1 Sound I 3.2 Sound II 3.3 Infra Red 3.4 Radio Waves & Microwaves I 3.5 Radio Waves & Microwaves II 3.6 Radio Waves & Microwaves 1II 3.7 Light 3.8 Light & Sight I 3.9 Light & Sight II

3.10 UV and X-rays

3.11 Nuclear Radiation I

3.12 Nuclear Radiation II

3.13 Nuclear Radiation III

Waves & RadiationStudy Guide

Section 1 - Sound

At level 4, by the end of this section you should be able to:

1. State what sound energy can and cannot travel through.

2. Give one example of a use for ultrasound.

3. Give the name of high frequency sounds beyond the range of human hearing.

.4. Give two examples of noise pollution.

6. Give examples of sound levels of some everyday sounds.

7. State that excessive noise can damage hearing.

Additionally, at Credit level you should also be able to:

8. In addition to 3 above, explain a use for ultrasound in medicine.

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Section 2 –Radio Waves & MicrowavesA lot of the modern telecommunications systems use radio waves or microwaves to carry the information between thetransmitter and receiver. To understand how these systems work, we have to first understand how the waves that carrythe information behave. You will find out about the behaviour of waves in this section.

The first man-made satellite, “Sputnik I”, was launched in 1957. Nowadays, several satellites are used to transmitthousands of phone calls and many television channels around the world (and all at the same time!)

In this section you will find out about the use of satellites to enable communication with all parts of the world, andabout the aerials used to send and receive signals over long distances.

At Level 4, by the end of this section you should be able to:

1. State the purpose of the curved reflector on certain aerials.

2. Explain the effect the curved reflector has on the received signal.

3. Describe one use of curved reflectors in telecommunications.

4. Say how a satellite’s height affects the time it takes to complete an orbit around the earth.

5. Explain the meaning of the word period.

6. State the meaning of a geostationary satellite.

7. Describe how geostationary satellites and dish aerials can be used to allow satellite television broadcasting.

8. Describe how geostationary satellites and ground stations make intercontinental communications possible.

Additionally, at Level 5 you should also be able to:

9. Carry out calculations involving the relationship between speed (v), distance (d) and time (t) in problems onmicrowaves, television and radio waves.

10. Carry out calculations involving the relationship between speed (v), wavelength (λ) and frequency (f) formicrowaves, television and radio waves.

11. Explain some of the differences between radio bands in terms of source strength, ability to diffract,reflection, etc.

12. Explain how wavelength affects radio reception in terms of diffraction.

13. In addition to 1 above, explain the action of curved reflectors on certain transmitters.

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Section 3 – The Use of Thermometers


1. State that a thermometer needs to have some physical property that changes with temperature and is easilymeasurable.

2. Describe the uses of infrared .

3. State that infra red is heat radiation.

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Section 4 – Light


1. State what is meant by the term ‘optical fibre’.

2. Describe one practical use of optical fibres in telecommunications and Medicine.

3. State that both electrical cable and optical fibres can be used in telecommunication systems.

4. State that light can be reflected.

5. Describe how a ray of light is reflected from a flat mirror with the help of the Law of Reflection.

6. State that light signals pass along an optical fibre at very high speeds.


7. Compare the properties of electrical cables and optical fibres.

8. Explain what is meant by reversibility of light.

9. Describe how an optical fibre transmission system works.

10. Carry out calculations using d=vt in problems on light travelling through optical fibres.

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Section 5 – Light and SightMost humans would agree that sight is their most important sense. Unfortunately, not everyone is born with perfecteyesight. However, physics can help people here too. In this section, you will study light, the human eye, some of itsdefects and how we can cure them.


1. Describe how the eye focuses light onto the retina.

2. State what is meant by refraction of light.

3. Draw diagrams to show the change in direction of light as it passes from (a) air to glass, and (b) glass to air.

4. Describe the shape of a convex and a concave lens.

5. Describe how these lenses affect parallel rays of light.

6. Describe how the orientation of the image on the retina compares to the object being looked at.

7. Use a ray diagram to show how an inverted image is formed on the retina.

8. Describe a simple experiment to find the focal length of a convex lens.

9. Give the meaning of long sight and short sight.

10. State that long and short sight can be corrected using lenses.

11. State that fibre optics can be used to transmit cold light into the body.


12. Use correctly in context the following terms: angle of incidence; angle of refraction; normal.

13. Use a ray diagram to show how the lens of the eye forms an image of a distant object.

14. Use a ray diagram to show how the lens of the eye forms an image of a near object.

15. Use the equation P = 1/f (where P is the power of a lens and f is its focal length).

16. In addition to 10 above, explain the use of lenses to correct long and short sight.

17. Explain how fibre optics is used in the endoscope.

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Section 6 - Ultra Violet and X-raysThe electromagnetic spectrum is a large family of waves with similar properties – for instance, they all travel at thespeed of light. Although similar in some senses, they are very different in others. .


1. Describe uses for the lasers.

2. Describe uses for x-rays.

3. State that photographic film can be used to detect x-rays.

4. Describe uses of ultraviolet..

5. State the dangers of too much exposure to ultraviolet radiation.


6. Describe the advantages of computerised tomography.

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Section 5 – Nuclear Radiation Radiation is a bit of a mixed blessing. In large quantities, it kills. In smaller quantities, it may be linked with certainforms of cancer. However, if it used properly, radiation is a very useful tool for physicists.

In this section, you will find out about both the benefits and the dangers of radiation, and how we detect it.


1. Say what radiation can do to living cells.

2. Describe one medical use for radiation based on the fact that it can destroy cells.

3. Describe one medical use for radiation based on the fact that it is easy to detect.

4. State the range of alpha (α), beta (β) and gamma (γ) radiations, and say how easily each can be absorbed.

5. Say what happens to radiation energy as it passes through a material.

6. Describe a model of the atom, using protons, neutrons and electrons.

7. Say which of the three ionising radiations produce the greatest ionisation density.

8. Give one example of a way in which radiation affects non-living things.

9. Give the units of the activity of a source.

10. State what happens to the activity of a source as time passes.

11. Describe the safety precautions necessary when dealing with radioactive substances.

12. Give the units of dose equivalent.

Additionally, at Level 5, you should also be able to:

13. Explain the meaning of the term ionisation.

14. In addition to 8 above, describe how one of the effects of radiation is used as a detector for radiation.

15. State the meaning of the term half-life.

16. Describe a method of measuring the half-life of a source.

17. Use information from a graph or table to calculate the half-life of a source.

18. Carry out half-life calculations.

19. State that dose equivalent takes account of the type of radiation and the energy of the radiation.

20. State that the biological effect of radiation depends on the dose equivalent and the type of tissue absorbingthe radiation.

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Section 1 - Sound

Sound is caused by vibrations.

Sound can travel through solids, liquids and gases, but not a vacuum

Noise Levels

Noise levels are measured in decibels , dB.

Regular exposure to noise levels above 90 dB (e.g. pneumatic drills or heavy traffic) can cause damage to hearing.

Typical noise levels : 0 dB Threshold of hearing60 dB Normal conversation95 dB Heavy lorry100 dB Pneumatic drill130 dB Jet engine140 dB Pain threshold

Ultrasound

Ultrasound is sound with a frequency above the range of human hearing. (above 20 000 Hz)

The Ultrasound Scanner

An ultrasound scanner can be used to examine the inside of a patient (e.g. an unborn baby

inside the mothers womb).

Ultrasonic waves are directed into the patient and reflect off objects inside the patient. It takes different times for the sound waves to

return from different depths and so an image of the patient can be built up using a computer.

A layer jelly is placed on the skin to prevent sound waves reflecting off the skin.

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Waves & RadiationSummary Notes


Page 10

Speed, Distance and Time(radio, television and microwaves)

speed =distance

time

sm/s

m

v t

d

d = v t

v = dt

t = dv

The Wave Equation(radio, television and microwaves)

speed = frequency x wavelength

mm/s

Hz

f λ

v

v = f λ

f = vλ

λ = vf

Section 2 - Radio Waves & Microwaves

Curved Dishes - Receivers

Curved reflectors are used to increase the strength of a received signal from a satellite or other source. The curved shape of the reflector collects the signal over a large area and brings it to a focus. The detector is placed at the focus so that it receives a strong signal

detector placed at focus

signals from a distant source

Mobile telephones, radio and television are all examples of long distance communication that do not require any cables between transmitter and receiver. All these methods of communication use waves to carry the signals. Mobile phones use microwaves to carry the signals, radio uses radio waves and television uses television waves. Microwave, radio and television waves all travel at very high speed (300,000,000 m/s in air).

Different radio transmitters can be identified by their different frequency or wavelength values (e.g. Radio 1 has a frequency of 99.5 MHz and Radio 4 LW has a wavelength of 1500 m)

Radio Waves, Television Waves and Microwaves

Curved Dishes - Transmitters

Curved reflectors are also used on certain transmitters to transmit a strong, parallel beam of signal. In a dish transmitter the signal source is placed at the focus and the curved shape of the reflector produces a parallel beam of signal.

signal source placed at focus

parallel beam of signal


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Diffraction

Diffraction is the bending of light around obstacles. All waves diffract to some extent, but longer wavelengths diffract more than shorter wavelengths.

Radio waves have a longer wavelength than television waves and therefore can bend round obstacles such as hills, buildings or trees more easily. Therefore radio reception is better than television reception in such areas

long wavelengthlots of diffraction

short wavelengthlittle diffraction

geostationary satellite

ground station

ground station

Satellites

The time taken for a satellite to complete one orbit of the Earth depends on it’s height above the Earth; the higher the orbit of the satellite the longer it will take to orbit.

Geostationary satellites take 24 hours to orbit the Earth. This is the same time that Earth takes to complete one rotation and so the satellite always remains above the same point on the Earth’s surface.

Ground stations send signals to the satellite using a curved dish transmitter to transmit a strong signal. At the satellite the signal is collected by a curved dish receiver, then amplified and finally retransmitted (at a different frequency) back to the ground using another curved dish transmitter.

With three geostationary satellites placed in orbit around the equator worldwide communication is permitted with each satellite communicating with ground stations on different continents.

In satellite television systems the signal from the satellite is broadcast over a wide area and collected by dish aerials on peoples homes.

Radio and Television Bands

Band Range Use Properties

ELF (Extra Low Frequency) 30 to 3,000 Hz submarines pass through water

LF (Low Frequency) 3 to 300 KHz long distance radio communication reflect off ionosphere

HF (High Frequency) 0.3 to 30 MHz local radio communication travel close to ground

VHF (Very High Frequency) 30 to 300 MHz broadcast FM radio short range

UHF (Ultra High Frequency) 300 to 3,000 MHz television travel in a straight line

Microwaves > 3,000 MHz satellites and mobile phones pass through ionosphere

Section 3 - Infra-Red

bulb

liquid(mercury or alcohol) scale narrow tube

glass

Liquid-in-glass Thermometer

The liquid inside the thermometer expands when it is heated. It’s volume increases and it rises up the tube.

The liquid expands more than the glass

A thermometer requires some measurable physical property that changes with temperature.

Type of thermometer Property that changes

liquid-in-glass volume of liquiddigital resistance of thermistor

crystal strip crystals have different melting pointsrotary different rates of expansion in bimetallic strip

Infrared voltage of thermopilethermocouple voltage produced

Types of Thermometer

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Waves & Radiation Summary Notes

Infrared

Infrared radiation is simply heat radiation with a wavelength longer than that of visible light.

Infrared radiation is used by physiotherapists to speed up the recovery of injured muscles and tissues.

Infrared radiation is also used in a thermal imaging camera where objects at different temperatures show up as different colours on a picture called a thermogram. Uses Of InfraredMedicine: Tumours are warmer than surrounding tissue and therefore show up on a thermogram.Night VisionInfrared can be used to amplify light in a low-light situation to enable video recording and image capturing.MeteorologyWeather satellites use infrared technology to determine water temperature and cloud formations.Art HistoryInfrared lights can be used to look under layers of painting to determine if there are older layers underneath.


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Principle of Reversibility.

If the direction of a ray of light is reversed it will follow same path, but in the opposite direction

Reflection

Light can be reflected as shown below :

i = angle of incidencer = angle of reflection

normal

ri

mirror

When light is reflected from a plane (flat) mirror it is found that the angle of incidence is equal to the angle of reflection. This is known as the law of reflection.

An optical fibre is a long, thin thread of glass through which light can travel. Light signals can travel along an optical fibre at very high speed (around 200,000,000 m/s). Optical fibres can carry telephone signals and modern telephone systems consists of both optical fibres and electrical cables.

Optical Fibres

Optical fibres have many advantages over electrical cables. These include :

1) smaller in size2) cheaper to make3) lighter4) greater signal capacity

(more information transmitted)5) higher signal quality6) less energy loss per km

(less repeater station required)7) are not affected by interference8) not easily ‘tapped’.

However, light signals in optical fibres only travel at 200,000,000 m/s as opposed to almost 300,000,000 m/s for electrical signals in a wire.

Optical fibres are also more difficult to join together than electrical cables

Advantages of Optical Fibres

Optical Fibres and Endoscopes

In optical fibres only light is transmitted along the fibre, but not heat. The optical fibre is therefore said to transmit ‘cold light’.

Optical fibres are used in endoscopes to view the insides of a patient without the need for surgery.

In an endoscope one bundle of fibres is used to carry ‘cold light’ down into the patient. A second bundle is then used to send the image back to the surgeon’s eye. The bundles are flexible and so can be moved around inside the patient.

Section 4 - Light

Section 4 - Using the SpectrumLasers

A laser is a very intense beam of light that carries a great deal of energy.Medicine Lasers are used for eye surgery, to remove birthmarks and to remove cancerous tumours.Welding and Cutting The beam of a laser can be focused to a microscopic dot of extremely high energy density for welding and cutting.Surveying and Ranging Helium-neon and semiconductor lasers have become standard parts of the field surveyor's equipment. A fast laser pulse is sent to a corner reflector at the point to be measured and the time of reflection is measured to get the distance. Barcode Scanners Supermarket scanners typically use helium-neon lasers to scan the universal barcodes to identify products.

LASER

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Operation of an Optical FibreOptical fibres work because of total internal reflection. This is when all the light is reflected inside the glass and none escapes into the air. Total internal reflection occurs when the angle of the incident ray is greater than an angle known as the critical angle (about 42o for glass). In this way light can travel great distances through optical fibres without ever leaving the fibre

Operation of an Optical Fibre

Optical fibres work because of total internal reflection. This is when all the light is reflected inside the glass and none escapes into the air. Total internal reflection occurs when the angle of the incident ray is greater than an angle known as the critical angle (about 42o for glass). In this way light can travel great distances through optical fibres without ever leaving the fibre

large angle of incidence all light reflected

along fibre

An Optical Fibre Transmission System

In an optical fibre transmission system, such as a telephone system, electrical signals are converted into pulses of light by laser. These pulses of light then travel down the optical fibre and at the other end are converted back into electrical signals by a photodiode. The laser and photodiode are so fast acting that hundreds of different signals can be transmitted down the same fibre simultaneously.

Section 5 - Light & Sight

The Eye

Light is focused on the retina of the eye by the cornea and lens.

Most of the refraction takes place at the cornea.The lens changes shape and allows the eye to focus on objects at different distances.

iris

pupil

cornea

lens

optic nerve

retina

Lenses

A convex (converging lens) causes rays of light to be brought to a focus.

A concave (diverging lens) causes rays of light to spread apart.

Focal length

i = angle of incidencer = angle of refraction

Focal length is the distance between a lens and the point where parallel rays of light are brought to a focus.

The focal length of a convex lens can be measured experimentally by placing the lens in front of a screen and moving the lens until a sharp image of a distant object is obtained on the screen, then measuring the distance from the lens to the screen (this is the focal length).

focal length

Refraction

i = angle of incidencer = angle of refraction

Refraction is the bending of light as it passes from one material into another.

When light passes from air into glass it bends towards the normal and when it passes from glass into air it bends away from the normal.

ri

air glass

normal

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Image Formation in the Eye

The eye forms an image which is upside-down (inverted) and back-to-front (laterally inverted).

The image is also smaller than the object being viewed.

Sight Defects

People with short-sight are unable to focus on distant objects clearly. Short-sight can be corrected by using a concave lens.

People with long-sight are unable to focus on close objects clearly. Long-sight can be corrected by using a convex lens.

Short-Sight Long-Sight

Short-sight occurs because parallel rays of light from a distant object are brought to a focus in front of the retina. (Image is short of retina)

Long-sight occurs because diverging rays of light from a nearby object are brought to a focus behind the retina (Image is long of retina)

Short-sight can be corrected by placing a concave lens in front of the eye to diverge the rays of light entering the eye

Long-sight can be corrected by placing a convex lens in front of the eye to converge the rays of light entering the eye

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Section 6 - UV and X-rays

X-raysX-rays can be used to find broken bones.

A beam of X-rays is aimed the patient. Since bone is more dense than the surrounding tissue it absorbs more X-rays. A ʻshadowʼ is therefore cast on the photographic film placed behind the patient. The X-rays blacken the film, so the bones show up white and any breaks as dark lines.

Photographic film is frequently used as a detector of X-rays.

X-ray source

arm bone

arm muscle

photographicplate

dark on plate

llight

Computerised Tomography

In computerised tomography a series of horizontal X-ray images are taken of the body. A computer then uses these ‘slices ‘ to build up a 3-dimensional (3-D) picture of the body. This enables small tumours to be found very accurately and provides more detailed images than a conventional X-ray pictures.

Ultraviolet

Ultraviolet radiation is radiation with a wavelength shorter than that of visible light.

Medicine:Ultraviolet radiation is used to treat skin problems and to sterilise medical instruments.ForensicsForensic scientists will use ultraviolet lights to look for clues at a crime scene.CD/DVD PlayersCD and DVD players use lasers, which are a form of ultraviolet light, to read information off of the disc.

Other uses for UV light include getting detecting forged bank notes in shops, and hardening some types of dental filling.

Excessive exposure to ultraviolet radiation (e.g. from the Sun) can cause skin cancer.

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Industrial ImagingWelders use X-ray technology to inspect tightly welded seams that appear perfect for bubbles and other anomalies.

AstronomyX ray telescopes study high-energy X-rays coming from exotic sources such as black holes, exploded stars and the hot gas in galaxy clusters.

Section 7 - Nuclear RadiationUses of Radiation

Radiation can kill or damage living cells.

Nuclear radiation is used in medicine to sterilise medical instruments by killing germs. It can also be used to kill cancerous cells either by placing an alpha source next to the tumour or by firing a beam of gamma rays at the tumour from a variety of different directions (therefore only the tumour receives a large radioactive dose and the surrounding tissue is relatively unharmed). Radiation is also used for diagnosis. A radioactive tracer (a gamma source) is injected into the patient. The tracer is carefully chosen so that it will collect in the organ being studied and an image of the organ can be then be taken with a gamma camera.

The Atom

An atom is the smallest particle into which matter can be divided. It is made up of a central nucleus with orbiting electrons.

electrons

nucleus containing protons and neutrons

The nucleus contains positively charged protons and uncharged (“neutral”) neutrons. The nucleus makes up nearly all the mass of the atom and contains all the positive charge

The electrons orbit the nucleus at high speed. They are negatively charged and much lighter (1/2,000 th) than neutrons or protons.

An atom is normally electrically neutral as it has the same number of negative electrons orbiting the nucleus as positive protons in the nucleus.

Types of Radiation

There are three types of nuclear radiation. These are alpha (α), beta (β) and gamma (γ)

Whenever radiation passes through a material (medium) some of it’s energy is absorbed by the material. The amount of absorption depends on the type of radiation and the material it is passing through.

Type Range in Air Absorbed by

α 20 cm of air sheet of paper

β a few metres 2-3 mm Aluminium

γ not absorbed 2-3 cm Lead

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Health PhysicsSummary Notes

Smoke alarms contain a weak source made of Americium-241.Alpha particles are emitted from here, which ionise the air, so that the air conducts electricity and a small current flows. If smoke enters the alarm, this absorbs the a particles, the current reduces, and the alarm sounds.

Thickness controlIn paper mills, the thickness of the paper can be controlled by measuring how much beta radiation passes through the paper to a Geiger counter. The counter controls the pressure of the rollers to give the correct thickness. SterilisingEven after it has been packaged, gamma rays can be used to kill bacteria, mould and insects in food. This process prolongs the shelf-life of the food, but sometimes changes the taste.

Activity

The activity of a radioactive source is the number of atoms that decay each second (number of radioactive particles released each second).

The activity of a radioactive source is measured in Becquerels, Bq.

The activity of a radioactive source decreases with time.

Half-life

The half-life of a radioactive source is the time taken for it’s activity to half.

The half-life of a radioactive source can be measured by taking measurements of the activity of the source at regular intervals of time using a Geiger-Muller tube and counter.

sourceGeiger-Muller tube

counter

Background activity is then subtracted from each reading and a graph of activity against time is drawn.

activity

time

The time taken for the activity to half can then be established from the graph

Half-life calculations

Example 1:

If a 8,000 Bq source of activity has a half-life of 6 days what activity will it have 18 dayslater ?

18 days = 3 x 6 days= 3 half-lives

18,000 4,000 2,000 1,0002 3

The activity after 18 days is 1,000 Bq

Example 2:

Calculate the half-life of a source that decreases in activity from 32 kBq to 8 kBq in 24 days.

132 16 82

2 half-lives = 24 days 1 half-life = 12 days

The half-life of the source is 12 days

Safety

Safety precautions need to be taken when handling radioactive materials. These include :

• Always handle with forceps• Point source away from body• Store in lead container• Label all sources• Wash hands after use

Dose equivalent

The dose equivalent of a radioactive source is a measure of the biological risk of the source and is measured in Sieverts, Sv.

The biological effect of radiation depends on:• the type of absorbing tissue• the type of radiation• the total energy absorbed The dose equivalent takes into account the type

of radiation and the total energy absorbed.

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Absorption of radiationWhen considering the radiological effects of radiation, we must take into account not only the total energy absorbed but the mass of the material within which it is absorbed, e.g. for a dental X-ray, the absorbing mass would be the mass of tooth, gum, jaw and cheek.Absorbed dose, D, is the energy E absorbed by unit mass.Absorbed dose is measured in grays. 1 gray (Gy) = 1 joule per kilogram.

D = E m

The absorption of energy by a substance depends on:o the nature and thickness of the substanceo the type of radiationo the energy of the particles or photons of the radiation.Alpha radiation is absorbed within a fraction of a mm of tissue, which gives a very high absorbed dose because of the small absorbing mass.

The biological effects of radiationAll ionising radiation can cause damage to the body. There is no minimum amount ofradiation which is safe. The risk of biological harm from an exposure to radiation depends on:•the absorbed dose•the kind of radiation•the body organs or tissue exposed.

The body tissue or organs may receive the same absorbed dose from alpha or gammaradiation, but the biological effects will be different. To solve this problem a radiation weighting factor,WR is used which is simply a number given to each kind of radiation as a measure of its biological effect.Some examples are given below. WR Type of radiation

1 beta particles / gamma 10 Protons and Fast Neutrons

20 alpha particles

Dose equivalentWhen scientists try to work out the effect on our bodies of a dose of radiation they prefer totalk in terms of dose equivalent. The dose equivalent H is the product of D and WR.

Dose equivalent = absorbed dose x radiation weighting factor

H = DWRThe dose equivalent is measured in sieverts, Sv.

Example A worker in the nuclear industry receives the following absorbed doses in a year.30 mGy from gamma radiation, WR = 1300 mGy from fast neutrons, WR = 10Calculate the dose equivalent for the year. H = DWRfor gamma H = 30 x 10-3 x 1 = 30 x 10-3 Svfor neutrons H = 300 x 10-6 x 10 = 3.0 x 10-3 Sv total H = 30 x 10-3 + 3.0 x 10-3 = 33 x 10-3 Sv


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Background radiationEveryone is exposed to background radiation from natural and from man-made radioactivematerial. Background radiation is always present. Some of the factors affecting backgroundradiation levels are:

• Rocks which contain radioactive material, expose us to ionising particles• Cosmic rays from the sun and outer space emit lots of protons which causeionisation in our atmosphere• Building material contain radioactive particles and radioactive radon gas seeps upfrom the soil and collects in buildings, mainly due to lack of ventilation.• The human body contains radioactive potassium and carbon• In some jobs people are at greater risk. Radiographers exposed to X-rays used in hospitals and nuclear workers from the reactor.

Natural radiation is by far the greatest influence on our exposure to background radiation.

NUCLEAR REACTORSAdvantages of using nuclear power to produce electricity•Fossil fuels are running out, so nuclear power provides a convenient way ofproducing electricity.•A nuclear power station needs very little fuel compared with a coal or oil-firedpower station. A tonne of uranium gives as much energy as 25000 tonnes of coal.•Unlike fossil fuels, nuclear fuel does not release large quantities of carbon dioxideand sulphur dioxide into the atmosphere,which are a cause of acid rain.Disadvantages of using nuclear power to produce electricity•A serious accident in a nuclear power station is a major disaster. British nuclearreactors cannot blow up like a nuclear bomb but even a conventional explosioncan possibly release tonnes of radioactive materials into the atmosphere. (TheChernobyl disaster was an example of a serious accident.)•Nuclear power stations produce radioactive waste, some of which is very difficultto deal with.•After a few decades nuclear power stations themselves will have to be disposed of.


Nuclear fissionAn atom of uranium can be split by a neutron. This can produce two new nuclei plus theemission of neutrons and the release of energy.

Chain reactionOnce a nucleus has divided by fission, the neutrons that are emitted can strike otherneighbouring nuclei and cause them to split releasing energy each time. This results in whatis called a chain reaction as shown below.

In a controlled chain reaction, on average only one neutron from each fission will strikeanother nucleus and cause it to divide. This is what happens in a nuclear power station. In anuncontrolled chain reaction all the neutrons from each fission strike other nuclei producing alarge surge of energy. This occurs in atomic bombs.

Nuclear fusionFusion occurs when two light nuclei combine to form a nucleus of larger mass number, e.g. the fusion of two deuterium nuclei (an isotope of hydrogen) to form helium.

Once again, there is a decrease in mass in the fusion process and the energy released is produced as kinetic energy of the fusion products.

The energy released by the sun and other stars is produced by nuclear fusion.

1 Echo sounding equipment on a ship receives sound pulses reflected from the sea bed 0.04s after they were sent out by the ship.

Speed of Sound in water = 1 500m/s(a) How long does it take a sound pulse to reach the sea bed?(b) What is the depth of water under the ship?

2 An ultrasound unit produces sound of frequency 5 MHz (5 000 000 Hz) The speed of sound in soft tissue is 1 500 m/s(a) Calculate the wavelength of these waves in soft tissue.(b) An echo is detected 0.0001 s After the pulse is sent out .To what depth has the sound penetrated?

3 Which is faster: audible sound or ultrasound?

4 Which has the longer wavelengths: audible sound or ultrasound?

5 Match the following Statements with the correct endings, then copy.

Sound is produced by frequencyThe number of vibrations per second is the ultrasonicSound levels are measured in VibrationsFrequencies above about 20 000 Hz are decibels

6 Match the typical sound to its sound level, then write out the table in descending order of loudness

Typical sound Decibels

Busy street 120Inside a boiler factory 70Heavy truck 10Normal conversation at 1m 90Whisper 60Leaves rustling in the wind 30

Waves & RadiationQuestions

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7. Draw three full waves and mark on your diagram:(a) the wavelength (b) the amplitude

8. Two sound waves are examined using a microphone attached to a signal generator. The traces appear as shown:

Which wave has (a) the bigger amplitude?(b) the bigger frequency?

9. Copy and complete the following table by marking in the correct symbols and units.

frequency

wavelength

velocityssecondttime

SymbolUnitSymbolQuantity

10. This diagram represents some water waves. If 80 crests pass a pointin 20 seconds, find:(a) the frequency(b) the wavelength(c) the speed of the waves.

11. This diagram represents some water waves which are being made at a rate of 50 per second.

1m

(a)• What is the frequency? . . . . . -(b) Find the wavelength.(c) Calculate the speed of the waves.


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12. Some water waves in a canal travel straight along the canal at 0. 5 metres per second and have a wavelength of 2 metres.If you were standing on the bank, how many waves would pass you in one second?

13. A wave generator in a tank produces water waves at a frequency of5 Hz. If the speed of the waves is 0.5 m/s , find their wavelength.

14. If waves break onto a beach once every 2 seconds and there is a distance of 4 metres between the wave crests, how fast are the waves travelling?

15. A wave of frequency 10 Hz travels at 45 cm/s .(a) How many peaks pass each point every second?(b) What is the distance between successive troughs?

16. 120 crests of a long wave train pass one point in 30 s. A few of the waves are shown in this diagram.

Find the waves’ (a) frequency(b) wavelength(c) speed

17. If the frequency of waves in a tank is 10 Hz and the wavelength is4 cm, what is the velocity of the waves?

18. If the frequency of waves in a pond is 5 Hz and the wavelength is7 cm, what is the velocity of the waves?

19. The velocity of sound is 330 m/s. If the frequency of a sound wave is 30 Hz find the wavelength.

20. Find the wavelength of a water wave of frequency 40 Hz travelling at120 cm/s

21. The velocity of waves in a swimming pool is 0.6 m/s and the wavelength of each wave is 5 cm. What is their- frequency?

22. If Sound waves travel at 1500 m/ s in water, what is the wavelength of a 30 Hz note in water?

23. A water wave of wavelength 3 cm travels 20 cm in 5 s.(a) What is the velocity of the wave?(b) What is the frequency of the wave?


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24. A water wave of wavelength 5 cm travels 120 cm in 1 minute.(a) What is the velocity of the wave?(b) What is the frequency of the wave?

25. Copy and complete the table:

5 x 1012 3 x 1083 x 1083 x 106

3300.253.5220

300250250

speed, v (m/s)wavelength, λ (m)Frequency, f (Hz)

26. What is the wavelength of a wave of frequency 0.1 Hz and speed 4 m/s ?

27. Water waves in a test tank are travelling at 10 cm/s and are generated with a frequency of 15 Hz.

(a) How many peaks are produced per second?(b) What is the distance between successive troughs?

28. If the speed of sound in air is 320 m/s . calculate(a) the wavelength of a note whose frequency is 240 Hz. (b) the frequency of a sound whose wavelength is 2.4 m.

29. The highest note any human can hear is about 20 kHz. What is the wavelength of this note? (Take the speed of sound as 320 m/s (

30. A signal generator produces 25 waves every 0. 1 s. If the velocity of sound is 330 m/s what is the wavelength of the wave

31. A wave takes 0.75 seconds to. travel 300 m. The generator making the wave vibrates 120 times per minute. Find the wavelength of the wave.

32. A water wave (X) has a wavelength of 6 cm and a frequency of 50 Hz. Another water wave (Y) travels 250 m in 1 minute 40 s. Which wave travels faster — and by how much?

33. Water waves travel from one side of a pond to another, a distance of 18 m, in 4.5s. The distance between two successive wave crests is 8 cm. What is the frequency of the waves?

34. How far will a radio signal travel in 5 seconds?

35 How far will a radio signal travel in 1 minute?

36 How long would it take a radio signal to travel the 400 000 000 m from the earth to the moon?


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37 (a) Can water waves bend round edges into shadow areas? (b) What is this bending called?

38 Can microwaves behave in a similar way when they pass obstacles?

39 Copy and complete these diagrams:

When water waves of long wavelength pass a barrier, they produce the following pattern:

If the wavelength is reduced, the pattern changes to:

40 Which bend more when diffracted, long or short wavelengths?

41 TV waves usually have a shorter wavelength than radio waves. Why is it that, in mountainous regions, TV can sometimes not be received although there is good radio reception?

42 Which of the following stations is likely to be best received in hilly country?Radio 1 (285m) Radio 2 (433m)Radio 3 (247m) Radio 4 (1500m)

43. Two rays of light strike a mirror as in the diagram below. Copy and complete the diagram showing:(a) how the waves travel after reflection, (b) where the normal(s) to the mirror are situated.

44. A motorist depends entirely on her rear view mirror to know the position of traffic behind her. Draw a ray diagram to show how light from behind the car can enter the motorist’s eyes.


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45 How far does light travel through air in 10 seconds?

46 How Far does light travel through an optical fibre in 10 seconds?

47 How long does light take to travel 350 000 000 m through air?

48 How long does light take to travel through an optical fibre cable1 000 000 km long?

49 How long does a signal take to travel along an optical fibre link between two towns which are 400 km apart?

50 A signal takes 3 milliseconds to travel adistance of 600 km along a certain optical fibre link. At what speed does the light travel along this link?

51 A signal travelling at a speed of 2 x 108 m/s takes 2.5 milliseconds to reach the end of a length of optical fibre cable. How long is the cable?

52 Signals travel at a speed of 2 x 108 m/s along a transatlantic optical fibre cable. How long is the cable if it takes 25 milliseconds for the signal to travel along it?

53. Five parallel rays of light are incident on a mirror as shown in the diagram below

(a) Copy and complete the diagram showing what happens to the light rays. after reflection.(b) Explain in detail how this experimental arrangement could be produced in the laboratory.

54 (a) Draw the rays of light produced by the. lamp in this searchlight.

(b) What other things can you think of which also use a concave mirror to produce a beam of light?


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55 Diagram shows a mercury in a glass thermometer

(a) What temperature is the thermometer recording ?(b) Explain why the mercury level will not immediately rise to its final steady level when the thermometer is placed in a warm liquid.

56 Liquid hydrogen boils at -250ºC while liquid nitrogen boils at -196ºC. Which of the two liquids has the higher boiling point?

57 What is the temperature difference between the inside of a house at 16ºC and the outside when the temperature is -5 C?

58 Use the words and phrases below to describe the operation of a liquid in glass thermometer.

mercury expands mercury rises

59 Match the following statements with the correct endings, then copy.

Heat flows from hot to 0ºCNormal body temperature is hotnessThe melting point of ice is 37 CSolids expand when cold objectsThe boiling point of water is heatedTemperature is a measure of 100ºC

60 Match the type of thermometer to the measurable physical quantity which changes in each case then copy

Mercury thermometer Colour change with temperatureCrystal strip thermometer Different amounts of expansionRotary thermometer Liquid expansion on heating

61 What is a bimetallic strip?

62 Explain why a bimetallic strip bends when heated


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63 In the diagram: should the metal that expands the most be on the inside or outside of the coil?

64 Mercury Thermometer Alcohol ThermometerAdvantages Disadvantages Advantages Disadvantages

Thread easy to see. Freezes at -39 Freezes at -115 Has to be colouredto be seen easily.

Conducts heat well. Thermometer Expansion greaterhazardous if than mercury

Responds quickly broken. . Thread hasto temperature Wider tube can tendency tochanges Expensive. be used. break.

Use the data in the above table to explain why an alcohol filled thermometer might be preferred to a mercury filled thermometer by an arctic explorer.


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68 Draw a convex lens. Why is it also called a converging lens?

69 Draw a concave lens. Why is it also called a diverging lens?

70 Neatly copy and complete the following diagrams to show the path of the light ray in and after passing through the glass shape:

71 What is meant by refraction of light

72 A beam of light passes from air to glass as shown

Neatly copy and complete the diagram showing the direction of the beam in the glass. Add the normal to the diagram , the angle of incidence and, the angle of refraction.

73 A person who can see objects clearly only if they are close to him, is said to be short sighted. Far away objects appear blurred because light from them comes to a focus in front of the retina .

What type of lens could be used to correct short sightedness?


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74 A long sighted person can see objects clearly only if they are far away. Nearby obj ects appear blurred because light from them comes to a focus behind the retina

What type of lens should be used to correct long sight?

75 Explain, with the use of a diagram, your choice of lenses for questions 73 and 74.

76 Describe with the aid of diagrams how you would use a converging lens

(a) to ignite a match in strong sunlight.(b) to produce a parallel beam of light from an electric lamp.

77 a) Copy and complete the following diagram of the electromagnetic spectrum.

GammaRays

UltraViolet

VisibleLight

Radio& TV Waves

b) What speed do electromagnetic waves travel at?c) Infrared radiation has a frequency of 1 x 1013 Hz and travels at 3 x 108 m/s. Calculate the wavelength of the radiation.

78 How can excessive exposure to ultra violet radiation be dangerous to a person?


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79 What happens when X-rays enter the body?

80 How are X-rays used in C.A.T. scanners?

81 What are the advantages of Computed Tomography?

82 a) Describe how X-rays are detected by photographic film.b) A toddler swallows a one pence coin. Will this produce a light or dark image on the X-ray?

83 Healthy lungs always appear fairly dark on X-ray transparencies. Why?

84 a) A hospital may use a C.A.T. scanner . What does C.A.T. stand for?

b) Explain how a C.A.T. scanner produces images and how these are better than ordinary X-rays.

85 An atom contains three different particles. List these and the charge on each.

86 Copy and complete this data table, put a tick (√ ) if the radiation can get through and an cross (X) if it can be absorbed:

gamma

beta

alpha

3cm Lead3mm AluminiumPaperRadiation

87 A scientist is given an unmarked box containing a radioactive sample. He finds that the radiation emitted will pass through paper but will not pass through a 3mm sheet of aluminium .What sort of radiation is being emitted by the source?

88 (a) Which radioactive particle is a fast moving electron? (b) Which radioactive particle has a positive charge? (c) Which radiation has no charge?


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89 A Geiger-Muller tube is connected to a counter. Although there are no radioactive sources in the laboratory the counter shows a reading. What causes this reading?

90 What unit is used to measure the activity of a source?

91 What happens to the activity of a source as time passes?

92 Explain what is meant by the statement sodium has a half-life of 14 days.

93 Suppose the half-life of a particular radioactive substance is 30 s, and its measured activity is 900 decays per second from the instant a clock is started.a) What would you expect the activity to be 30 s later?b) What would you expect the activity to be 60 s after the clock was started?

94 A radioactive substance has a half-life of 6 hours. What fraction of the original activity is left after one day?

95 An isotope has a half-life of 50s. How long does it take for the activity to fall to 1/64 of the starting value?

96 The activity of a source starts at 80 MBq. After 10 days it has fallen to 2.5 MBq. calculate the half-life.

97 What is the half-life of a radioactive substance if its activity falls from 400 kBq to100 kBq in 12 days?

98 What is the half-life of a radioactive isotope if the activity falls from 3200 kBq to200 kBq in 200 days?

99 On a day when the background count is 15 counts per minute a radioactive substance gives a count rate of 335 counts per minute. What is the half-life of the substance if the count rate 8 minutes later is 95 counts per minute?

100 The half-life of Cobalt-60 is 5 years. 15 years ago a school bought a source of activity 300 kBq. What would its activity be now?

101 The half-life of a radioisotope is 30 days. One hundred and twenty days after its manufacture its activity is measured as 100 kBq. Find its initial activity.


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102 The table below shows how the count rate of a radioactive source varies with time. Correction has been made for background radiation.

81218284572Count rate(per second)

1086420Time(minutes)

a) Draw a graph and determine the half-life of the source.b) What will be the count rate after 5 half-life periods.

103 The measured activity of a radionuclide was taken at 3-day intervals. The following readings are uncorrected for background radiation.

30395271100145Count rate(per minute)

15129630Time(days)

The count rate was measured again 2 months after the first reading and found to be 12 counts per minute.

a) Estimate the background count rate.b) Draw a graph and calculate the half-life of the radionuclide.

104 Which of the two carbon isotopes carbon12 or carbon14 can be used in carbon dating?

105 What is the half-life of carbon14 ?

106 A piece of wood preserved in a peat bog is found to have a ratio of carbon14 to carbon I 2 of only 1/16th of that found in the atmosphere. Estimate the age of the wood.

107 The amount of carbon14 left after 7 half-lives is only just detectable. What is the maximum age that can be estimated using carbon dating?

108 Explain why radiocarbon dating is no use for estimating the age of coal, which was formed about 400 million years ago.

109 State one example of the effect of radiation on non-living things .

110 Why is it important that the dose of radiation used in cancer treatment isa) not too high?b) not too low?


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111 Describe uses of radiation which are based on the fact that radiation a) can kill cells,b) is easy to detect.

112 What unit is used to measure the dose equivalent?

113 if you have been using radioactive sources, what should you do before eating? Why?

114 How is a radioactive source stored to keep it safe?

115 In particular, which part of the body must the source never be pointed at?

116 . Can you think why young people should not be exposed to radiation?

117. What do we mean by the activity of radioactive material?

118 What does the risk of biological harm from radiation depend on?

119 A worker spends some time in an area where she is exposed to the following

radiations:

thermal neutrons = 8 mGy radiation weighting factor= 3

fast neutrons = 40 mGy radiation weighting factor= 10 .

(a)Calculate the dose equivalent for each type of neutron.

(b)What is the total dose equivalent for the exposure?

120 What does the radiation weighting factor for each radiation give us an indication of?

121 In the course of his work an industrial worker receives a dose equivalent of 200 mSv.

Determine the absorbed dose if he is exposed to alpha particles, with a radiation

weighting factor of 20.


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122 An unknown radioactive material has an absorbed dose of 500 mGy and gives a dose equivalent of 1 mSv. Calculate the radiation weighting factor of the material. 123 A patient receives a chest X-ray with a dose equivalent of 2.0 mSv. If the quality factor of the X-ray is 1, calculate the absorbed dose of the patient. 124 A lady has a dental X-ray which produces an absorbed dose of 0.3 mGy. Calculate the dose equivalent of this X-ray. 125 A nuclear worker is exposed to a radioactive material producing an absorbed dose of 10mGy. She finds that the material emits particles with a radiation weighting factor of 3. Calculate the dose equivalent for this exposure. 126 A physics teacher uses a gamma source in an experimental demonstration on absorption The teacher receives an absorbed equivalent of 0.5 mSv. Calculate her absorbed dose if the radiation weighting factor for gamma radiation is 1. 127 (a)Alpha particles produce a dose equivalent of 50 mSv from an absorbed dose of 2.5mGy. Calculate the radiation weighting factor of the alpha particles. . (b)Why does exposure to alpha radiation increase the risk of cancer more than X-rays or gamma rays? 128 The unit for absorbed dose is the gray, Gy. Explain this term and give another unit for absorbed dose. 129 What is background radiation and from where does it originate?


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Waves & RadiationHomework Exercises

Homework 3.1 - Sound I

1. Answer the following questions in your jotter.

(a) What is sound produced by? (1/2)(b) What do we call the number of vibrations per second? (1/2)(c) What do we call sound frequencies greater than 20 000 Hz? (1/2)

2. In each of the following situations, state whether the sound is travelling through a solid, a liquid or a gas.

(a) Native Americans could hear horses a long way off by putting their ear to the ground. (1/2)(b) Dolphins use high-pitched sounds to locate fish for food. (1/2)(c) A teacher shouts at you for not attempting your homework! (1/2)

3. In the Star Wars films (and similar), there are many loud explosions as spaceships blow up. In reality, youwouldn't hear the explosions at all. Why not? (1)

4. Give a non-medical use for ultrasound. (1)

5. A teacher puts a bell inside a large jar, and switches it on. His pupils can hear the bellclearly. The teacher then pumps the air out of the jar using a vacuum pump.

(a) What would happen to the sound? (1)(b) Why would this happen? (1)

6. (a) Name one use for ultrasound in medicine. The diagram may give you a hint! (1)(b) Explain why ultrasound waves are used for this purpose rather than x-rays. (1)

Total 10 marks

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Homework 3.2 - Sound II

1. Copy the following table, and use the figures below to show the typical sound level of each sound: (3)

10 dB, 30 dB, 60 dB, 70 dB, 90 dB, 120 dB

TYPICAL SOUND SOUND LEVEL (dB)Busy streetInside a boiler factoryHeavy truck passing byLeaves rustling in the windWhisperNormal conversation at 1 metre

2. Give two examples of noise pollution. (2)

3. (a) In what way could a noisy factory cause harm to its workers? (1)(b) How could the workers avoid this harm? (without quitting their jobs!) (1)

4. Ear plugs and earmuffs are used to protect hearing.

(a) What do these protectors do to the sound’s energy? (1)(b) Suggest a material that could be used for the filling of the protectors. (1)

5. On the decibel scale, every 10 dB represents an effective doubling of the perceived loudness of sounds.More simply, a sound of 50 dB will sound twice as loud to you compared to a sound of 40 dB.

How many times louder than leaves rustling in the wind does normal conversation sound? Use values fromthe table in question 1 to help you. (1)

Total 10 marks

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Homework 3.3 - Infra Red

1. For each type of thermometer, state the physical quantity that changes as the temperature changes. (4)TYPE OF THERMOMETER MEASURABLE PHYSICAL QUANTITY

Mercury thermometerCrystal strip thermometerRotary thermometerDigital thermometer

2. (a) What is a bimetallic strip? (1)(b) Explain why a bimetallic strip bends when heated. (2)

3. (a) Name the two liquids most commonly found in liquid-in-glass thermometers. (1)(b) Describe how a liquid-in-glass thermometer works. (2)

Total 10 marks

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Homework 3.4 - Radio Waves & Microwaves I

1. Copy the table below and fill in the symbol, unit and definition for each term. (3)WAVE TERM SYMBOL UNIT DEFINITION

frequencywavelengthspeed

2. The questions below refer to this diagram.

(a) Calculate the wavelength of the waves shown.Give your answer in metres (1)(b) If the waves took 6 seconds to travel this distance, what is their frequency? (1)(c) What is the amplitude of these waves? (1)(d) Use the wave equation to calculate the speed of the waves. (2)

3. A wave of frequency 8 Hz has a wavespeed of 16 m/s.What is its wavelength? (2)

Total 10 marks

6km

2 m

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nm

Line


Homework 3.5 - Radio Waves & Microwaves II

1. (a) Name three forms of long range communication that don't use cables to carry the signals. (1)(b) How are signals transferred from transmitter to receiver for these systems? (1)

2. (a) Virgin Radio broadcasts on a frequency of 1215 kHz. What is the wavelength of these radio waves? (2)(b) Name two quantities that can be different for different radio signals. (1)

3. The table below gives information about the main radio and television waves:

FREQUENCY RANGE FREQUENCY WAVELENGTH SPREAD WAVEBAND RANGE MAIN USES

30 Hz - 3 kHz ELF >100 000 m --- --- Links to submarines3 kHz - 30 kHz VLF 100 000 - 10 000 m --- >1500 km long range navy & army use

30 kHz - 300 kHz LF 10 000 – 1000 m long wave >1500 km long range navy & army use300 kHz - 3 MHz MF 1000 – 100 m medium wave <1500 km sound broadcasts3 MHz - 30 MHz HF 100 – 10 m short wave world wide sound broadcasts

30 MHz - 300 MHz VHF 10 – 1 m ultra short just beyond horizon high quality sound300 MHz - 3000 MHz UHF 1 - 0.1 m --- horizon television or mobile link

(a) What are ELF radio waves used for? (1/2)(b) Northsound Radio uses a frequency of 96.9 MHz. Which waveband does Northsound use? (1/2)(c) Calculate the wavelength of Northsound Radio waves. (2)

4. A house in a hilly region can't get a good reception on the television, but radio reception is perfect. Explainwhy this is. (2)

Total 10 marks

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Homework 3.6 - Radio Waves & Microwaves III

1. Aerials picking up signals from a long distance away often have a curvedreflector attached to them.

(a) What is the purpose of the curved reflector? (1)(b) How does it do this? Include a diagram with your answer. (2)

2. The period of a geostationary satellite is 24 hours.

(a) Explain what a geostationary satellite is. (1)(b) What is meant by the word period? (1)(c) How is a satellite’s period affected by its height above the Earth? (1)

3. Draw a diagram to show how a telephone signal could be sent to America from Britain without the use ofundersea cables. (2)

4. Copy this diagram and complete it to show how the curved reflector helps produce a parallel beam ofmicrowaves: (2)

Total 10 marks

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Homework 3.7 - Light

1. (a) What is the law of reflection? (1)(b) Illustrate your answer to part (a) with a neat, labelled diagram. (2)

2. (a) What is an optical fibre? (1)(b) Give one example of a use for optical fibres in a telecommunications system. (1)

3. Give two advantages of optical fibres over electrical cable. (1)

4. Copy the diagram, and complete it to show the path taken by the ray of light.Include normals and mark all angles. (2)

5. An optical fibre is used to carry a telephone message to the USA from Scotland. It travels 5000 km. Thelight signals travel at a speed of 2 x 108 m/s. How long will this take? (2)

Total 10 marks

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Homework 3.8 – Light and Sight I

1. Copy and complete the eye diagram to the right to show howa healthy eye would focus the rays of light. (1)

2. A ray of light passes from air to glass as shown:

(a) Copy and complete this diagram to show what happens to the ray in the glass. (1)(b) What is this effect called? (1)(c) Add the normal to the diagram, and label the angle of incidence and angle of refraction. (2)

3. (a) Draw a convex lens, and show how it affects parallel rays of light. (2) (b) Draw a concave lens, and show how it affects parallel rays of light (2)

4. (a) Draw a convex lens, and show how it affects parallel rays of light. (1)(b) Draw a concave lens, and show how it affects parallel rays of light. (1)

Total 10 marks

air glass

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Homework 3.9 – Light and Sight II1. A girl wants to find the focal length of a convex lens she has found in the classroom. She uses light from the

window in her experiment.

(a) What other equipment will she need to do her experiment? (1)(b) What measurement should she make? (1)(c) Why does she use light from the window rather than from the classroom lights? (1)

1. Copy and complete the table below (4)(b) A spherical concave lens has a power of -10 D. What is its focal length? (1)

3. Copy the table below, and fill in the blanks to give information about short & long sight: (3)EYE DEFECT DESCRIPTION LENS USED

Short sightLong sight

2. (a)Copy and complete the eye diagram to the right to show howthe eye of a short-sighted person would focus the rays oflight. (3)

(b)Copy and complete the eye diagram to the right to show how

the eye of a long-sighted person would focus the rays of light. (3)

Total 10 marks

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Homework 3.10 – UV and X-rays

1. When tissue absorbs laser light, the light energy is converted to heat energy. This makes it very useful inmedicine

Give two ways in which laser light is used in medicine. (1)

2. (a) Give two uses for x-rays . (1)(b) Explain why x-rays are used for these purpose (2)(c) What detector is used to pick up the x-rays in hospitals? (1)

3. (a) Thermal cameras do not detect light like normal cameras. Whichelectromagnetic waves do they detect? (1)

(b) What is the picture called taken by a thermal camera? (1)

4. What is the main danger of overexposure to ultraviolet radiation? (1)

5. Give two advantages of a CT scan over an ordinary x-ray photograph. (2)

Total 10 marks

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Homework 3.11 – Nuclear Radiation I

1. (a) Describe a medical use of radiation that is based on the fact that it can kill cells. (1)(b) Describe a medical use of radiation that is based on the fact that it is easily detected. (1)

2. Copy and complete the following table, using a '' if the radiation can pass through, and a '' if theradiation is absorbed. (3)

RADIATION PAPER 3mm ALUMINIUM 3cm LEAD

Alpha (α)Beta (β)Gamma (γ)

4. Draw a diagram of a model of the atom. Carefully label the nucleus, and a proton, a neutron, and anelectron. (3)

7. Describe how a Geiger-Muller tube detects radiation. (2)

Total 10 marks

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Homework 3.12 – Nuclear Radiation II

1. Copy and complete the following table, matching the correct units to the quantities listed. (1)

QUANTITY UNIT

ActivityDose Equivalent

2. In 1969, a new man-made element called Rutherfordium was created in America. Some tests were done todiscover its half-life. The element's starting activity was measured as 20 480 Bq, and 18 seconds later, it haddropped to just 320 Bq.

Calculate the half-life of Rutherfordium from these figures. (3)

3. Living plants incorporate a radioactive isotope of carbon (C14) into their living tissue. This radioactivecarbon is always found in the same ratio to ordinary carbon (C12) in something that is alive, but once it dies,the ratio of C14 to C12 decreases.

By comparing the ratio of the two types of carbon the age of a piece of dead plant material can becalculated. The half-life of C14 is approximately 6000 years. That is, after 6000 years, the ratio of C14 to C12

will be half the original value.

The amount of C14 left after 7 half-lives is only just detectable. This puts a limit on the maximum age thatcan be estimated using this technique.

(a) What is the half-life of C14? (1)(b) A piece of wood preserved in a peat bog is found to have a ratio of C14 to C12 of only 1/16

th that found ina living tree. Estimate the age of the wood. (2)

(c) What the maximum age that can be estimated using this technique? (1)

8. List two safety precautions necessary when dealing with radioactive sources. (1)

9. How are hospital staff protected from radiation and x-rays when they work with these resources? (1)

Total 10 marks

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HEALTH PHYSICS Homework Exercises

Homework 3.13 – Nuclear Radiation II 1. A sample of tissue exposed to radiation receives an absorbed dose of 0.13mGy. The radiation weighting factor for this radiation is 9. Calculate the dose equivalent for this sample. (2 ) 2.A technician handling an alpha emitting source estimates that his hand received an absorbed dose of 5x10-5Gy. The mass of the technicians hand is 500g. (a) Calculate the total energy absorbed by his hand. ( 2) (b) Using information from the table below calculate the dose equivalent received by his hand. (2)

Type of radiation Radiation Weighting Factor Alpha 20 Beta 1 Gamma 1 X rays 1 Slow neutrons 2.3

3. When living tissue is exposed to a source of ionising radiation a quantity is found from dividing the energy absorbed during the exposure by the mass of the tissue. What is the name of this quantity and the unit it is measured in ? (1) 4. State the two factors affecting biological damage risk which equivalent dose takes into account. ` (2) 5. What does the radiation weighting factor measure ? (1) Total 10 marks

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paisley grammar school physics - t2tw · paisley grammar school physics department name: class:...

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