Topic Six - Waves

Question 1

What is amplitude?

Answer 1

It is the maximum displacement of a point on the wave from its undisturbed position.

Question 2

What is wavelength?

Answer 2

The distance between the same point on two adjacent waves.

Trough to trough.

Question 3

What is frequency?

Answer 3

The number of complete waves passing a certain point per second.

Question 4

What is frequency measured in?

Answer 4

Hertz

Question 5

What is a period of a wave?

Answer 5

The amount of time it takes for a full cycle of the wave to pass a point.

Question 6

What is a transverse wave?

Answer 6

The vibrations are perpendicular to the direction of the energy transfer.

Question 7

What are examples of transverse waves?

Answer 7

Electromagnetic waves, light
Ripples and waves in water
A wave on a spring.

Question 8

What are longitudinal waves?

Answer 8

The vibrations are prallel to the direction of energy transfer.

Question 9

What are wavelengths in longitudinal waves?

Answer 9

From compression to compression

Question 10

What are compressions in longitudinal waves?

Answer 10

When the spring tightens.

Question 11

What are rarefractions in longitudinal waves?

Answer 11

When the spring stretches.

Question 12

What are examples of longitudinal waves?

Answer 12

Sound waves in air

Shock waves-seismic waves

Question 13

How can you measure the speed of sound?

Answer 13

Set up the oscilloscope so the detected waves at each microphone are shown as separate waves.
Start with both microphones next to the speaker then slowly move one away until the two waves are aligned on the display, but have moved exactly one wavelength apart.
Measure the distance between the microphones to find one wavelength.

Question 14

How can you measure the speed of water ripples using a lamp?

Answer 14

Dim the lights and turn on the lamp.
Youll see a wave pattern made by the shadows of the wave crests on the screen below the tank.
The distance between each shadow length is equal to one wavelength.
Measure the distance between shadow lines that are ten wavelengths apart then divide it by ten to find an average wavelength.
Use the equation to find the speed of the waves.

Question 15

How can you find the speed of waves on springs?

Answer 15

Turn on the signal generator and vibration transducer. The string will start to vibrate.
To change the length of the wave adjust the frequency on the signal generator.
Keep adjusting it until there is a clear wave on the string.
The frequency needed will depend on the length of the string between the pulley and the transducer.
Measure the wavelength of the wave. Do this by measuring all the half wavelengths on the string in one go, then divide by the number of half wavelengths and times by two to get the full wavelength.

Question 16

What is refraction?

Answer 16

When light waves are bent when they enter a new material.

Question 17

What happens when a wave arrives at the boundary of two different materials?

Answer 17

The wave can be absorbed by the second material.
Transfers energy to the materials energy stores, often a thermal energy store.
The wave is trasmitted through the second materials. It carries on travelling through the new material which often leads to refraction.
The wave is reflected-this is where the incoming wave is neither absorbed nor transmitted but instead is sent back away from the second material.

Question 18

What is optical density?

Answer 18

A measure of how quickly light can travel through it.

The higher the optical density, the slower a wave travels through it.

Question 19

What happens during refraction?

Answer 19

When a wave crosses a boundary between two materials it changes speed.
It the wave is travelling along the normal it will change speed but its not refracted.
If a wave hits the boundary at an angle it changes direction-its refracted.
If a wave bends towards the normal it slows down but if it bends away from the normal it speeds up.
How much is refracted depends on the density of the two materials.

Question 20

How are radio waves made?

Answer 20

Alternating currents are made up of oscillating charges.
As the charges oscillate they produce electromagnetic waves.
The frequency of the waves produced will be equal to the frequency of the alternating current.
You can produce radiowavrd using the aternating current.
Th electrons oscillate to create the radio waves is called a transmitter.
When the radio waves reach the reciever they are absorbed.
The energy transferred by the waves is transferred to the electrons in the material of the reciever.
The energy causes the electrons to oscillate and the reciever generates an alternating current.

Question 21

What happens to long wave radio waves?

Answer 21

They can be transmitted from all around the world.

That is because the long wavelengths diffract around the curved surface of the earth.

Question 22

How are microwaves used by satellites?

Answer 22

Satellites.
The signal from a transmitter is transmitted into space.
It is where its pickef up by the satellite reciever dish orbiting above the earth.
The satellite transmits the signal back to earth in a different direction where its recieved by a satellite dish on the ground.

Question 23

How are microwaves used in microwave ovens?

Answer 23

The microwaves need to be absorbed by water molecules in food so they use a different wavelength to satellites.
The microwaves penetrate a few cm into the food before being absorbed and transferring the energy they are carrying to the water molecules causing the water to heat up.
The water molecules transfer energy to the redt of the molecules in the food by heating which quickly cooks the food.

Question 24

How is infrared radiation used to moniter temperature?

Answer 24

Infrared radiation is given out by all objects so the hotter the object the more IR radiation it gives out.
Infrared cameras can be used to detect infrared radiation and monitor temperature.
The camera detects the IR radiation and turns it into an electric signal, which is displayed on a screen.
The hotter an object the brighter it appears.

Question 25

How can infrared radiation increase temperature?

Answer 25

Absorbing IR radiation causes objects to get hotter.
Food can be cooked using IR radiation, the temperature of the food increases when it absorbs IR radiation.
Electric heaters heat a room in the same way.
Electric heaters emit infrared radiation and it is absorbed by objects and the air in the room.

Question 26

How is visible light used to trasmit data in fibre optic cables?

Answer 26

Optical fibres are thin glass or plastic fibres that can carry data over long distances as pulses of visible light.
They work because of reflection. The light rays are bounced back and forth until they reach the end of the fibre.
Light is not easily absorbed or scattered as it travels along a fibre.

Question 27

How does ultraviolet radiation give you a suntan?

Answer 27

Ultraviolet radiation is produced by the sun and exposure to it is what gives people a suntan.
UV lamps are used to give them an artifical suntan.

Question 28

What can ultraviolet radiation to be used for?

Answer 28

Security pens can be used to mark property with your name.

Under UV light the ink will glow but it is invisible otherwise

Question 29

How are xrays and gamma rays used in medicine?

Answer 29

Xrays pass easily through flesh but not through denser materials like bones and metal.
So the amount of radiation absorbed is what gives you an xray image.
Used to treat people with cancer. High doses kill all living cells so they are directed towards cancer cells to avoid killing healthy cells.

Question 30

How do people protect against xray and gamma radiation?

Answer 30

Wear lead aprons
Stand behind a lead screen
This keeps exposure to a minimum.

Question 31

What do low frequency waves do?

Answer 31

They dont transfer much energy so pass through soft tissue without beinng absorbed.

Question 32

What do high frequency waves do?

Answer 32

They transfer lots of energy so can cause lots of damage.

Question 33

What are the effects of UV radiation?

Answer 33

Damages surface cells which can lead to sunburn and premature ageing.
Some serious effects are blindness and increased risk of skin cancer.

Question 34

What are the effects of xrays and gamma rays?

Answer 34

They are ionising radiation.
They carry enough energy to knock electrons off atoms.
This can cause gene mutation or cell destruction and cancer

Question 35

How do objects absorb and emit infrared radiation?

Answer 35

The hotter an object is the more infrared rays it radiates in a given time.
An object thats hotter than its surroundings emits more than it absorbs as it cools down.
An object thats cooler than its surrounding absorbs more radiation than it emits as it warms up.
Objects at a constant temperature emit radiation at the same rate that they are absorbing it.

Question 36

What surfaces are better at emitting and absorbing infrared radiation?

Answer 36

A black surface and a matte surface are better at absorbing and emitting radiation.

Question 37

How can you investigate absorbtion with the melting wax trick?

Answer 37

Two ball besrings are each stuck to one side of a metal plate with solid pieces of candle wax.
The other sides of the places are faced towards the flame.
The sides of the playe facinf towards the flame each have a different surface colour.
One is matte black and the other is silver.
The ball bearing on the black plate ull fall first as the black absorbs more IR radiation.

Question 38

How can you investigate radiation emissions using a leslie cube?

Answer 38

Place an empty leslie cube on a heat proof mat.
Boil water in a kettle and fill the leslie cube with boiling water.
Wait for the cube to warm up then hold a thermometer against each of the vertical faces.
Hold an infrared detector at a set distance away from one of the cubes faces and record the amount of radiation it detects.
Repeat this for each of the cubes faces.
You should find you detect more from the black and matt surfaces.