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PHYSICS Mr. BALDWIN WAVES 14-Jan-14AIM: What is periodic or harmonic motion?

DO NOW

1. A mass is attached to a spring on a horizontal frictionless surface. The system is then compressed and released. Describe the motion of the mass.

2. A mass is attached to the end of a string (simple pendulum). The mass is slightly pulled from its rest position and released. Describe the motion of the pendulum.

3. What do both systems have in common?

HOME WORK: WkSh 19.2: Harmonic Motion Graphs

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What is Periodic Motion?What is Periodic Motion?

What would happen if you

slightly displace (push) the mass

attached to the spring on a

frictionless surface?

The mass vibrates or oscillates

back and forth over the same

path, each cycle taking the same

amount of time, the motion is

called periodic.

Look at the Compressed spring/Mass system again• What type of energy does the system possess when it is

compressed?

• spring potential energy

• What type of energy does the system possess when it passes through the equilibrium position?

• kinetic energy

• What type of energy does the system possess when it is stretched?

• spring potential energy

• What is happening to the system in terms of energy?

• It’s converting between spring potential and kinetic energy

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The Simple Pendulum

• ..\..\WHSAD PHYSICS 2013 2014\pendulum-lab_en.jar

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Look at the simple pendulum• What type of energy does the system possess when it is at

rest?

• No energy

• What type of energy does the system possess when it displaced from its equilibrium position?

• Potential energy

• What type of energy does the system possess when it is released and passes through its equilibrium position?

• Kinetic energy

• What is happening to the system in terms of energy?

• It’s converting between potential and kinetic energy

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Periodic Motion: Compressed Spring/Mass• Displacement is measured from the equilibrium point

• Amplitude (A) is the maximum displacement from the equilibrium point

• A cycle is a full to-and-fro motion; this figure shows half a cycle

• Period (T) is the time required to complete one cycle

• Frequency (f) is the number of cycles completed per second

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Property RelationsProperty Relations

• The frequency f is

inversely proportional to

the period T

• Unit of frequency is

called the Hertz (Hz)

1Hz = 1cycle/s

Tf

1

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PHYSICS Mr. BALDWIN WAVES 15-Jan-14

AIM: How can we describe a wave?

DO NOW

1. What are some things you know about a wave?

2. Light and heat energy comes to us from the Sun. How does it get here?

3. What is the name and call number of your favorite radio station?

4. Do you know what the call number represents?

HOME WORK: WkSh 20.1: Waves

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Wave Motion: Wave characteristicsWave Motion: Wave characteristics• A A wavewave is a periodic disturbance that transfers energy is a periodic disturbance that transfers energy

from one point to anotherfrom one point to another– ex. light, sound, (electromagnetic {E-M} waves)

• Water waves, sound waves, and light waves are very different from one another in various ways, but all have in common some basic properties:

– WavelengthWavelength

– FrequencyFrequency

– PeriodPeriod

– AmplitudeAmplitude

– Wave speedWave speed

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Wave characteristics

• Amplitude, A

•Frequency f and period T

• Wavelength,

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Wave PropertiesWave Properties• Wavelength is the distance between successive points

on a wave. Ex. distance between adjacent crests or troughs.– Meters (m)

• The frequency f of waves is the number of waves passing a particular point per second. – Hertz (Hz)

• The period T is the time needed for a one complete wave to pass a given point. – Seconds (s)

• The amplitude A of a wave is the maximum displacement on either side of its normal position of the wave.

Below is a snap shot of a wave travelling for 1 sec.

About how many waves do you see?

What is the period and frequency of the wave?

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CHECK

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Wave Property RelationsWave Property Relations

• The frequency is inversely proportional to the period– Hz = 1/s

• The wave speed is equal to the product between the frequency & wavelength– m/s

• Speed of light (E-M)– c = 3.0 x 108 m/s

• Range of visible light

: 380 - 720 nm.

1fT

v f

v vf

f

CHECK• What is a nm?

• 10 -9 m

• What are the call letters and numbers of your favorite radio station?

• 107.5WBLS

• Do you know what the numbers represent?

• frequency (in MHz)

• What is a MHz?

• 10 6 Hz

• What is the wavelength of such a wave?

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PHYSICS Mr. BALDWIN

WAVES 23-Jan-14AIM: How can the speed & type of a wave be

determined?

DO NOW1. What do waves transport?2. What do all waves have in common?3. What is the frequency of blue light that

has a wavelength of 480 nm?

HOMEWORK: Worksheet: 20.1 Waves

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RECALL: Wave Property RelationsRECALL: Wave Property Relations

• The frequency is inversely proportional to the period

• WAVE EQUATION: The wave speed is equal to the product between the frequency & wavelength

• Speed of light (E-M)

• ALTERNATE FORMS

1fT

v f

v vf

f

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Types of Waves: Transverse & Longitudinal

The motion of particles in a wave can either be

perpendicular to the wave direction (transverse) or

parallel to it (longitudinal).

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Transverse WavesTransverse Waves

• Transverse waves has propagations in both the horizontal & vertical directions but perpendicular to wave direction– ex. Light (E-M) waves

• Longitudinal waves have propagation in one direction only (Unidirectional). Particles vibrate parallel to wave direction– ex. Sound waves

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Longitudinal WavesLongitudinal Waves

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Sound waves are longitudinal waves: pressure waves

(Rarefaction)

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PHYSICS Mr. BALDWIN

WAVES 7-Feb-14AIM: How does sound travel?

DO NOW1. How is sound generated (created)?2. What is an echo?3. What type of wave is a sound wave?

Homework: In your own words, write a short ESSAY on the Doppler Effect (do not plagiarize) & WkShts 20.1 & 21.1

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Standing WaveStanding Wave

• A standing wave is generated in a pipe closed at one or both ends or on a string bounded on one or both ends.– ex. Organ pipe or guitar string

• A standing wave is generated by most musical instruments.

• Sound waves require the presence of matter in order to propagate. Light does not.

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Antinode: points that undergo maximum displacement

Node: points of zero displacement

What do you observe about the distance between nodes and antinodes?The distance between two consecutive nodes (or antinodes) in a standing wave is half the wavelength.

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Velocity of SoundVelocity of Sound

• Most sound are produced by vibrating objects, such as a cone of a loud speaker.

• Speed of sound depends on temperature

• CHECK…What is the speed of sound at 200C?

• Speed of sound at standard temperature & pressure

(STP - 200C & 1atm) vsound = 343 m/s

Cs Tv 6.0341

• Sound waves are described as pressure waves in a solid, liquid or gas

• Sounds waves are longitudinal waves

– The molecules in their path moves back and forth in the same direction as that of the wave

• The velocity of sound also depends on the density of the medium.

• WHY?

• The denser the medium the faster it travels.

– 1500 m/s in water; 5000 m/s in iron

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Velocity of SoundVelocity of Sound

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Frequency of SoundFrequency of Sound

• Range of Audible Frequency of sound (sound that humans can hear): 20 Hz – 20 kHz.

• Infrasonic frequency range < 20 Hz– Sources includes earthquakes, thunder, volcanoes,

heavy machinery• Ultrasonic Frequency range > 20 kHz

– Dogs & Bats hear in this range

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PHYSICS Mr. BALDWIN

WAVES 5-Feb-14AIM: How do you know a fire engine is

coming towards you? (What is the Doppler Effect?)

DO NOW: Describe what you observe as a siren approached you and when it goes away from you.

TURN IN • Your ESSAY on the Doppler Effect• Completed Worksheets 20.1 & 21.1

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Velocity of SoundVelocity of Sound

• How are sound waves produced?

• Most sound are produced by vibrating objects, such as a vibrating cone of a loud speaker.

• Speed of sound depends on temperature (0C)

• CHECK…What is the speed of sound at 200C?

• Speed of sound at standard temperature & pressure

(STP - 200C & 1atm) vsound = 343 m/s

Cs Tv 6.0331

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The Doppler EffectThe Doppler Effect

• The apparent change in the observed frequency of a wave between a moving source and observer.

s s

o

true frequency, f source velocity,v1

apparent frequency, f light or sound speed,c

1

so

s

ff

v

c

• It is applicable to any type of wave.

• Austrian physicist Christian Doppler (1803-1853).train sound clip

Simulations• physlet animation• http://www.walter-fendt.de/ph14e/dopplereff.htm

Analyze this.• If the observer & source is

moving apart, vs is positive

• If the observer & source is moving closer, vs is negative

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• The velocity of sound is about 340 m/s. What are the frequencies observed as a fire engine, with siren blaring at 200Hz and moving at 17 m/s, approaches and then passes you?

Sound

Source

Sourceobserved

vv

ff

1

DO IT YOURSELF

An ambulance is approaching a stationary observer. The siren of the ambulance emits a frequency of 480Hz and the speed of the ambulance is 50km/h(=13.88m/s).

What wavelength and frequency will the stationary observer hear when the ambulance is approaching? Assume T=20oC.

ADVANCE QUESTIONING

• Determine the wavelengths of the sound waves of the siren as the fire engine approaches and as it leaves.

• What are some common everyday uses of the Doppler Effect?

• Doppler Radar (Weather Systems)

• Red & Blue Shifts (Astronomy)

• Speed detection (Police radar)

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1. A physics student sitting on the beach notices that a wave hits the beach every 5.0 seconds, and the waves seem to be about 15m apart.

a. What is the frequency of the waves?

b. What is the period of the waves?

c. What is the speed of these waves?

2. What is the frequency of laser light that has a wavelength of 623nm?

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PHYSICS Mr. BALDWIN

WAVESAIM: What are the properties of

sound?

DO NOW1. Describe a longitudinal wave.2. Describe a transverse wave.

Homework: Handout

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PHYSICS Mr. BALDWIN

WAVES 11-Feb-14AIM: What happens when you exceed

the speed of sound? How loud is loud?

DO NOW: QUIZ: Handout

Homework: Handout

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The graph below displays how displacement varies with TIME when a wave passes a fixed point at a speed of 12.0 m/s. How many waves are there? What is the amplitude of the wave? Determine the frequency and wavelength of the wave based on the previous information.

(m)

t (s)

1 2 3 4 5 6 7 8 9 10 11 12 13

1

2

3

4

5

–1

–2

–3

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LOUDNESS• Noise is measured in

units called decibels (dB), on a scale from zero to 140. The higher the number in decibels, the louder the noise.

• For every 20 dB increase, a sound is twice as loud.

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OBSERVE

• What do you observe about the wave-fronts as the source approaches the speed of sound?

• http://dev.physicslab.

• org/asp/applets/doppler/default.asp

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The speed of sound• What is the speed of sound at STP?• The speed of sound in air is 343 meters per second at one

atmosphere of pressure and room temperature (20°C).• Convert this to mph (1mi=1609m)• (760 miles per hour)• An object is subsonic when it is moving slower than sound.• An object is transonic when it is moving at the speed of sound.

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• We use the term supersonic to describe motion at speeds faster than the speed of sound.

• A shock wave forms where the wave fronts pile up. • The pressure change across the shock wave is what

causes a very loud sound known as a sonic boom.

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Mach numberThe unitless Mach number was named after the Austrian

physicist Ernst Mach.

The Mach number is ratio of the speed of the aircraft to the speed of sound .

An airplane flying at less than Mach 1 is traveling at subsonic speeds; at about Mach 1, or transonic , it is at the speed of sound, and greater than Mach 1 is supersonic . An aircraft traveling at Mach 2 is traveling at twice the

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soundofSpeed

speedAircraftnumberMach

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Mach vs. Knot

• http://www.grc.nasa.gov/WWW/k-12/BGA/Corrine/mach_number_wks.htm

• http://www.grc.nasa.gov/WWW/K-12/WindTunnel/Activities/knots_vs_mph.html

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PHYSICS Mr. BALDWIN

WAVES 12-Feb-14AIM: What is light? What is the electromagnetic

(E-M) spectrum?

DO NOW: What are the colors of the rainbow?Why are they different?How is it that heat comes to us from the Sun?

Homework: Worksheet 24.1 - The Electromagnetic Spectrum

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Electromagnetic WavesElectromagnetic Waves

• The electromagnetic spectrum consists of all types of electromagnetic radiation

• Gamma rays, x-rays, ultraviolet radiation, visible light, infrared radiation, millimeter waves, microwaves, and radio waves are all electromagnetic waves that differ only in their frequencies & wavelengths.

• ALL Electromagnetic waves travel in a vacuum with the same speed of light. (300,000,000 m/s)

• Write this in scientific notation.

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Electromagnetic SpectrumElectromagnetic Spectrum

• Infrared radiation (IR)– created by molecular

vibrations

• Visible light (white light)– created by electron excitation

• Ultraviolet radiation (UV)– created by electron excitation

• X-ray radiation– created by high energy

electron excitation

• Gamma (γ) radiation – created within the atomic

nuclei by high energy nuclear processes

• Ionization Radiation is any radiation that is energetic enough to ionize biological matter.– Causes genetic mutation of

DNA

– Penetrate deep into matter

• As λ decreases, the f increases, and hence the energy E increases

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Components of Visible LightComponents of Visible Light

• White light is polychromatic:– Made up of different colors of light– RedOrangeYellowGreenBlueIndgoViolet

• Wavelength Range of visible light 400 – 700 nm (Nanometer: 1nm = 10–9m

• Write these values in scientific notation in meters• Determine the Frequency Range of visible light• f: 4.3 – 7.5 x 1014Hz

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PHYSICS Mr. BALDWIN

INTERFERENCE of WAVES 26-Feb-14AIM: How do waves behave when they

interact? (What is interference?)

DO NOW: Why do we hear beats when different keys on a piano are played at the same time?

HOMEWORK: Complete lab

Wave interference

• Wave interference is the phenomenon which occurs when two waves meet while traveling along in the same medium.

• The addition or combination of waves is called the principle of superposition

Principle of Superposition

These figures below show the sum of two waves. In (a) they add up constructively; in (b) they add up destructively; and in (c) they add partially destructively.

Interference of Waves

• The first addition of waves that will be described involves two waves that are in phase.

• This is referred to as constructive interference.

• A crest of one wave is positioned with the crest of the other wave. The same can be said for the troughs.

This represents the displacementby the white wave alone.This represents the displacementby the green wave alone.Since they are both displacementson the same side of the baseline,What do you think will happen?THEY ADD UPJust repeat this step for severalpoints along the waves.

• The next addition of waves that will be described

involves two waves that are out of phase.

• This is referred to as destructive interference.

This represents the displacement by the white wave alone.This represents the displacement by the green wave alone.Since the two displacements are on opposite sides of the baseline,the top one should be considered positive and the bottom one negative.Since they are both displacements on the opposite sides of the baseline, what do you think will happen?THEY CANCEL EACH OTHER.

• Finally we observe two waves that are

partially in phase. This is called partial

destructive interference.

• A different method of adding the waves will

be demonstrated.

By overlaying the constructive interference curve from a previous slide you can tell that the curve of this slide is not fully constructive interference.

From the baseline measure to the “white” wave. Then add this to the “green” wave. See animation. Note the white arrow would be zero in length here.

So zero added to the “green” wave would give

Zero white arrows added to “green” wave occur at these other locations.

Continuing on with this process gives

For your experiment today you will be given two waves that are interfering with each other.

You will construct the resultant waveform by techniques similar to what you have just seen in this presentation.

There are also some calculations that you must complete.

Interference Animation

BALDWIN 66

PHYSICS Mr. BALDWINGEOMETRIC OPTICS 24-Feb-14AIM: How does light behave when it is incident on

another medium? (What is reflection and refraction?)

DO NOW: What do you observe when a pencil or spoon is placed in a clear glass of water?

HOME WORK – Worksheets 23.1: The Law of Reflection & 23.2: Refraction

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ReflectionReflection

• Reflection: the return or change in direction of a wave (light or sound) at the same angle is called reflection

– Echo is sound reflected

Check!…What is the proposed path of the incident light?

Reflection: Law of ReflectionReflection: Law of Reflection

Law of reflection: the angle of reflection (that the ray makes with the normal to a surface) equals the angle of incidence.

angle of incidence = angle of reflection

ri

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RefractionRefraction• Refraction: the

change in direction and speed of a wave as it passes from one medium to another

– Bending of light as it passes through a prism

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Check!…What is the proposed path of the incident light?

RefractionRefractionLight changes direction (bends) when crossing a boundary from one medium to another. The angle the refracted refracted ray makes with the normal is called the angle of refractionangle of refraction.

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Light slows when traveling through a medium. The index of index of refraction refraction n n of the medium is the ratio of the speed of light in vacuum to the speed of light in the medium:

Index of RefractionIndex of Refraction

BALDWIN 72

PHYSICS Mr. BALDWINGEOMETRIC OPTICS Apr 19, 2023

AIM: What is Snell’s Law? (How do we determine how much a light ray bends when it enters a medium?)

DO NOW:

A ray of light enters into a piece of plexiglas. The refractive index of plexiglas is 1.51. What is the speed of light when it enters the plexiglas? Take the speed of light to be 3.0 x 108 m/s.

Homework: Handout – Snell’s Law Worksheet

Snell’s LawA relationship relating the index of refraction in a given a medium and incident light angle to the index of refraction in the new medium and the refracted light angle.

θ1

θ2

n1: index of refraction of medium 1n2: index of refraction of medium 2θ1: the angle of light in medium 1θ2: the angle of light in medium 2

n1

n2

Snell’s LawSnell’s Law• What do you observe as light enters a

medium of higher or lower refractive index?

• Light bends towards the normal when going from a medium with a smaller index of refraction to a larger index of refraction.

• Light will have the smaller angle in the medium with the greater index of refraction.

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LensesLenses

• A lens is a piece of transparent material shaped so that it can produce an image by refracting light that comes from an object

• Lenses are use in many optical devices such as eyeglasses, cameras, telescopes, etc.

– Converging lens is a lens that brings parallel beams of light to a single point called the focus.

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Converging Lens

• Diverging lens is a lens that spreads out parallel beams of light. The focus is on the same side as the incoming light.

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Diverging Lens