The World Communicates

Assumed Knowledge Domain: knowledge and understanding: Refer to the Science Years 7–10 Syllabus for the following: 5.6.1a) identify waves as carriers of energy 5.6.1b) qualitatively describe features of waves including frequency, wavelength and speed 5.6.1c) give examples of different types of radiation that make up the electromagnetic spectrum and identify some of their uses 5.6.4a) distinguish between the absorption, reflection and refraction of light and identify everyday situations where each occurs 5.9.1b) identify that some types of electromagnetic radiation are used to provide information about the universe 5.12a) describe some everyday uses and effects of electromagnetic radiation, including applications in communication technology.

Physics Stage 6 Syllabus

describe the energy transformations required in one of the following:

– mobile telephone – fax/modem – radio and television

describe waves as a transfer of energy disturbance that may occur in one, two or three dimensions, depending on the nature of the wave and the medium

identify that mechanical waves require a medium for propagation while electromagnetic waves do not

define and apply the following terms to the wave model: medium, displacement, amplitude, period, compression, rarefaction, crest, trough, transverse waves, longitudinal waves, frequency, wavelength, velocity

describe the relationship between particle motion and the direction of energy propagation in transverse and longitudinal waves

quantify the relationship between velocity, frequency and wavelength for a wave:

λfv =

• perform a first-hand investigation to observe and gather information about the transmission of waves in: – slinky springs – water surfaces – ropes or use appropriate computer simulations • present diagrammatic information about transverse and longitudinal waves, direction of particle movement and the direction of propagation

• perform a first-hand investigation to gather information about the frequency and amplitude of waves using an oscilloscope or electronic data-logging equipment

• present and analyse information from displacement-time graphs for transverse wave motion

•plan, choose equipment for and perform a first-hand investigation to gather information to identify the relationship between the frequency and wavelength of a sound wave travelling at a constant velocity

•solve problems and analyse information by applying the mathematical model of

to a range of situations

v = fλ

1. The wave model can be used to explain how current technologies transfer information

Communication

Communication is the transfer of information from a sender to a receiver through a medium. From this definition it can be seen that there are at least four essential components in any communications system: Sender: the source of the information Receiver: the destination of the information Information (message): what is being communicated Medium: the way in which the information is carried from the sender to the receiver

Communication

Humans are social animals and have successfully communicated through the spoken word, and then, as the use of written codes developed, through increasingly sophisticated graphic symbols. A messenger was required to carry the information in hard copy form and this carrier could have been a vehicle or person. There was, however, still a time limit and several days were needed to get hard copy information from one side of the world to the other.

electromagnetic spectrum The discovery of electricity and then the electromagnetic spectrum has led to the rapid increase in the number of communication devices throughout the twentieth century. The carrier of the information is no longer a vehicle or person — rather, an increasing range of energy waves is used to transfer the message. The delay in relaying signals around the world is determined only by the speed of the wave, and the speed and efficiency of the coding and decoding devices at the departure and arrival points of the message.

describe the energy transformations required in one of the following:

– mobile telephone – fax/modem – radio and television

Describe – provide characteristics and features.

Energy

Many situations in Physics are linked by the concept of energy. There are two ways of transferring energy, one by direct contact, as in a collision, the other by means of wave motion, as in the radiation of heat energy. Water waves are familiar to most people; other forms of waves include sound and light. Radio and television signals are transmitted by waves. Regardless of their form, all waves exhibit the same basic behaviour. An important aspect of all wave motion is that energy is transferred from one point to another without the transfer of matter.

describe the energy transformations required in one of the following:

– mobile telephone – fax/modem – radio and television

Energy transformations are necessary for communication to occur

Energy transformations—when energy is changed from one form into another—happen all around us. Electrical energy is transformed into other useful forms by devices such as light globes, speakers, motors and heaters. In modern communication devices a series of energy transformations is required in order to transfer information from one place to another. For example: Microphones transform sound energy into electrical signals. The reverse happens in speakers, where electrical signals cause a small diaphragm to

vibrate, in turn causing vibrations in the air particles, which then radiate out as sound energy. Wired telephone communication is carried by electrical signals through copper wires from

telephone to telephone. In radio, television and mobile telephones, electrical signals are used to modulate radio

waves so that information is sent from the aerial of the transmitting device to the aerial of the receiving device. However, mobile telephones do not connect with each other directly. Their signals go through the nearest base station and the telephone company’s wire and fibre optic networks to the base station that is closest to the other telephone.

describe the energy transformations required in one of the following:

– mobile telephone – fax/modem – radio and television

mobile telephone

describe the energy transformations required in one of the following:

– mobile telephone – fax/modem – radio and television

fax/modem

describe the energy transformations required in one of the following:

– mobile telephone – fax/modem – radio and television

Pathway of energy transformations when information is sent by fax or modem

Radio and Television

describe the energy transformations required in one of the following:

– mobile telephone – fax/modem – radio and television

Energy transformations when information is sent to a television set (radio communications occur in a similar manner without light energy)

describe waves as a transfer of energy disturbance that may occur in one, two or three dimensions, depending on the nature of the wave and the medium

Describe – provide characteristics and features.

Waves - a Definition Wave motion is the result of a periodic disturbance of a medium, or of space, by some form of vibration (or oscillation) which transmits energy away from the oscillating source of the wave. Consider what happens in the following situations: • a pebble is dropped into a pool of still water • a flag ripples in the breeze • the free end of a rope tied to a post is given a jerk. In each case a disturbance caused by a vibration travelled through a medium (the water, the cloth of the flag, the material of the rope). The medium moved up and down or back and forth but did not go along with the disturbance. Disturbances that travel through materials are waves. A wave can go from one place to another (through a medium) carrying energy with it. Wave motion is one of the most important means of transferring energy in the universe.

Waves in one dimension

You can make a wave travel along a rope or spring if one end is held firmly and the other end moved up and down as shown in the figure below. This wave transports energy through a material by the motion of a pulse or disturbance without a transfer of the material itself.

describe waves as a transfer of energy disturbance that may occur in one, two or three dimensions, depending on the nature of the wave and the medium

One-dimensional — In the case of a one-dimensional wave, the energy travels effectively in a straight line away from the source of the wave. e.g. sound confined to a tube such as a flute, didgeridoo or organ pipe; a vibration travelling along a string/spring, a laser beam (effectively one-dimensional)

Waves in two dimensions

Movement energy from one body can also be transferred to another without the bodies coming into direct contact. For example, a cork or fishing float dropped into a pond will vibrate up and down. When the cork bobs up and down in the still water, waves will be set up on the water surface and these waves will propagate out from the cork as shown in the figure.

describe waves as a transfer of energy disturbance that may occur in one, two or three dimensions, depending on the nature of the wave and the medium

Waves in two dimensions Two-dimensional — The energy associated with a two-dimensional wave spreads out in a plane or flat surface. e.g. surface water waves, the vibrating skin on a drum, surface earthquake waves.

Waves in three dimensions

One of the best examples of three–dimensional wave motion is the light from a globe suspended from a wire to the centre of an empty room. The light comes from the filament of the light globe yet the light illuminates the walls, floor and ceiling of the room. The sphere of light emitted from a globe.

describe waves as a transfer of energy disturbance that may occur in one, two or three dimensions, depending on the nature of the wave and the medium

Sirens are often located on towers above the ground to warn people higher in buildings, and on the ground in all directions from the tower. Three-dimensional — In the case of a three-dimensional wave, the energy spreads out into the space surrounding the source in all directions. e.g light from a candle or light bulb, sound in air, radio waves from a radio station’s transmitter, microwaves from a mobile phone.

identify that mechanical waves require a medium for propagation while electromagnetic waves do not

Identify – recognise and name.

Mechanical and Electromagnet waves

Waves come in many forms and can be classified in different ways. One way it to classify them as either: Mechanical waves OR Electromagnet waves

Mechanical waves, which require a medium, that is, a solid, liquid or gas, to transfer energy. Waves in the ocean convey the energy from the wind to the shore, perhaps thousands of kilometres away. Earthquake waves convey energy from the epicentre of the earthquake to the surface this energy is often clearly evident in the damage and destruction that such events can cause.

identify that mechanical waves require a medium for propagation while electromagnetic waves do not

Wave energy does not move matter from one place to another. As the wave passes, the material that makes up the medium that the wave is travelling in may be disturbed, but will settle back to its original position once the wave has passed. The wave will convey energy from one place to another

Building in Concepcion Chile, February 2010

Electromagnet waves (for example, light waves) do not require a medium for propagation. This is why light can travel through the vacuum of space from the Sun to the Earth (but sound can not). Electromagnet waves include: visible light, X-rays, gamma rays, radio waves, infrared ..etc

Mechanical and Electromagnet waves

identify that mechanical waves require a medium for propagation while electromagnetic waves do not

Mechanical and Electromagnet waves Electromagnetic waves are oscillating (changing back and forth) magnetic and electric fields at right angles to each other that ‘self-propagate’, that is, continue on, even through a vacuum. In 1864, James Clerk Maxwell (1831–1879) first proposed the existence of waves that could travel through empty space as oscillating electric and magnetic fields. Maxwell believed that a medium, or substance, called the luminiferous aether was needed for such waves to move through. These waves were believed to have similar characteristics to light. These electromagnetic waves were later shown to be capable of moving through empty space, a proposition put forward in 1905 by Albert Einstein (1879–1955) in his special theory of relativity.

identify that mechanical waves require a medium for propagation while electromagnetic waves do not

define and apply the following terms to the wave model: medium, displacement, amplitude, period, compression, rarefaction, crest, trough, transverse waves, longitudinal waves, frequency, wavelength, velocity

Define – state meaning and identify essential qualities.

The features of waves

•define and apply the following terms to the wave model: medium, displacement, amplitude, period, compression, rarefaction, crest, trough, transverse waves, longitudinal waves, frequency, wavelength, velocity

The wavelength of a wave is the distance between adjacent points of two waves that are ‘in phase’. In phase means these points have exactly the same motion at the same time. One wavelength is the distance between adjacent crests or tops of waves.

The amplitude is the maximum size of the particle displacement from the undisturbed state. The amplitude of a sound wave determines the volume (loudness) of the sound, while the amplitude of a light wave determines the brightness of the light

The frequency is the number of waves that pass a fixed point per second. The frequency is assigned a symbol, f, when used in equations. The frequency of waves is usually measured in cycles per second, or hertz (Hz). One hertz is one cycle or wavelength passing a point per second. The pitch of a sound wave is determined by a sounds frequency, colour also is determined by the frequncy of light

The medium is the material in which the wave is propagating. Electromagnetic waves do not require a medium.

The period is the time taken for one complete vibration. That is, the time from rest to the maximum distance from the undisturbed level, then to the lowest point and back again to undisturbed level. The period is related to the frequency by the relationship that the period is equal to the reciprocal of the frequency. The period has the symbol, T.

The wave speed is the speed of the wavefront moving forward. Wave speed has the symbol v.

Top of the wave

bottom of the wave

Displacement is the perpendicular Distance of a point in the medium From its rest position as a wave passes

describe the relationship between particle motion and the direction of energy propagation in transverse and longitudinal waves

Describe – provide characteristics and features.

Mechanical waves are classified as either transverse or longitudinal according to the direction of disturbance or vibration relative to the direction of energy flow through a material. • In a transverse wave, the particles of the medium vibrate in a plane that is perpendicular to the direction of propagation of the wave. • In a longitudinal wave, the particles of the medium vibrate in the same direction as the direction of propagation of the wave.

describe the relationship between particle motion and the direction of energy propagation in transverse and longitudinal waves •define and apply the following terms to the wave model: medium, displacement, amplitude, period, compression, rarefaction, crest, trough, transverse waves, longitudinal waves, frequency, wavelength, velocity

Rarefaction is the term for the regions in the medium that are stretched out or elongated as a longitudinal wave passes Compression refers to the regions in the medium that, as

a wave passes, become squashed or compressed

Classifying waves The vibration or disturbance producing

the wave may occur: • at right angles (90∞) to the direction of

wave propagation. These waves are called transverse waves

• in the same direction as the direction of

wave propagation. These waves are called longitudinal waves.

• present diagrammatic information about transverse and longitudinal waves, direction of particle movement and the direction of propagation

Representation of a transverse wave and its key features

Representation of a longitudinal wave and its key features

quantify the relationship between velocity, frequency and wavelength for a wave:

λfv =

Wave Equation

The distance a wave travels in one second can be found by multiplying the number of whole waves that pass a point in one second by the length of each of the waves. Stated mathematically, this is v = f λ. This equation is also known as ‘the wave equation’. It applies to all waves, whether they are mechanical or electromagnetic, transverse or longitudinal. For example, if five waves pass a point in the ocean each second, and they each have a wavelength of 20 m, then the waves must be travelling at 100 m s–1. v = f λ v = velocity, measured in m s–1

f = frequency, measured in Hz λ = wavelength, measured in m When applying v = f λ to any form of electromagnetic radiation, the speed, v, of the wave is taken as the speed of light, c, which is 3.00 × 108 m s–1.

quantify the relationship between velocity, frequency and wavelength for a wave:

λfv =

Example 1

A popular FM radio station transmits on a frequency of 104.9 MHz. What is the wavelength of these radio waves? f = 104.9 MHz = 104.9 × 10 6 Hz v = 3.00 × 10 8 ms-1

v = fλ Rearrange to make λ the subject λ = 3.00 × 10 8 ms-1 / 104.9 × 10 6 Hz = 2.86 m

quantify the relationship between velocity, frequency and wavelength for a wave:

λfv =

(Interestingly, you will notice the effect of this wavelength when you are driving among tall buildings in the city while tuned in to an FM radio station. When you are stopped at traffic lights, the station may ‘fade’ due to reflections from the buildings. Moving the car forwards or backwards as little as a metre may cancel this effect, bringing the car’s antenna back to a place where reception is full strength.)

Example 2 Compare the wavelength of an AM radio station with a frequency of 702 kHz to that of the FM radio station in the previous question.

quantify the relationship between velocity, frequency and wavelength for a wave:

λfv =

f = 702 kHz = 702× 10 3 Hz v = 3.00 × 10 8 ms-1

v = fλ Rearrange to make λ the subject λ = 3.00 × 10 8 ms-1 / 702× 10 3 Hz = 427 m The wave length for 104.9 MHz was 2.86 m compared to 427 m

Example 3 What is the frequency of red light with a wavelength of 620 nm?

quantify the relationship between velocity, frequency and wavelength for a wave:

λfv =

λ = 620 nm = 620 × 10 -9 m v = 3.00 × 10 8 ms-1

v = fλ Rearrange to make f the subject f = 3.00 × 10 8 ms-1 / 620 × 10 -9 m = 4.84× 10 14 Hz

Example 4 A tsunami wave is detected by an early warning buoy in the Pacific Ocean. It has a period of 50.0 s. Satellite tracking shows that the wavelength of the waves is 10.0 km. From this information, the speed of the tsunami in the ocean can be found. What is its speed?

quantify the relationship between velocity, frequency and wavelength for a wave:

λfv =

1st step f = 1/T = 1/50.0 s = 0.02 Hz Next v = fλ = 0.02 Hz × 10.0 × 10 3 m = 2.00 × 10 2 ms-1

Graphing Waves A good way to represent a wave is by using a graph. Imagine a floating cork bobbing up and down as a series of ripples move across the water surface (i.e. a periodic wave). If you graph the (up-down) displacement of the cork against time, the graph will look something like this:

• present and analyse information from displacement-time graphs for transverse wave motion

What you CAN read from a Displacement-Time graph: Amplitude. The vertical scale measures the displacement of the cork from the “equilibrium” position (i.e. the flat water surface). Period. Since the horizontal scale is time, you can easily read from the graph how long it takes for one complete up and down cycle. On this graph T = 0.8s From Period, calculate Frequency: f = 1 / T = 1 / 0.8 = 1.25Hz If the speed of the wave was known, then you could calculate the wavelength, or vice versa.

Example Consider the displacement-time graph shown

From the graph, find the wave’s: (a) Amplitude (b) displacement when t = 9.0 s (c) period, T

Given that the wave is travelling at 24.0 m s–1, calculate: (d) the wavelength of the wave (e) sketch the wave itself showing its amplitude and wavelength. (f) for different points labelled ‘X’, ‘Y’ and ‘Z’ on the sketched wave, show the directions in which these points are moving or are about to move.

Solutions (a) 4 m (the maximum displacement)

(b) 2.5 m (from the graph) (c) 8.0 s (the time taken for the wave to complete one whole oscillation) (d) As T = 8.0 s, f = 1/8.0 = 0.125 Hz then: v = f λ, so λ = v/f = 24.0 m s–1/0.125 Hz = 192 m

the chosen point ‘X’ is moving up as the next crest approaches from the left. Point Y is about to move up, while point Z is moving down. (Note that the wave is moving to the right, but the medium itself would be moving up and down.)

• perform a first-hand investigation to observe and gather information about the transmission of waves in: – slinky springs – water surfaces – ropes or use appropriate computer simulations

• perform a first-hand investigation to gather information about the frequency and amplitude of waves using an oscilloscope or electronic data-logging equipment

•plan, choose equipment for and perform a first-hand investigation to gather information to identify the relationship between the frequency and wavelength of a sound wave travelling at a constant velocity

Summary: Jacaranda

Questions: Jacaranda

Questions: Jacaranda

Questions: Jacaranda