Waves

Question 1

Give the equation for wave speed

Answer 1

wave speed (m/s) = frequency (Hz) x wavelength (m)
v= fλ
the symbol for wavelength is the greek letter lambda it looks like an upside down Y

Question 2

Describe a transverse wave and gives some examples

Answer 2

A wave in which the vibration causing the wave is at right angles to the direction of energy transfer.
Examples are water waves and lightwaves

Question 3

Describe a longitudinal wave and give an example

Answer 3

A wave in which the vibration causing the wave is parallel to the direction of energy transfer, sound waves are longitudinal.

Question 4

Explain the terms areas of compression and rarefaction

Answer 4

if a slinky is pushed backwards and forwards it vibrates parallel to the direction of energy transfer causing a longitudinal wave.
In some places the coils are pushed closer together (area of compression) and in others the coils are pulled apart (area of rarefaction)

Question 5

Explain the terms which are used to describe waves.

Answer 5

1. Amplitude (A) - the height from the middle of the undisturbed portion of the wave. Half the height between the trough and the peak.
2. Wavelength (λ) - the distance from peak to peak or trough to trough.
3. Frequency (f) - The number of waves produced every second, or passing a point every second, measured in Hertz (Hz).
4. Period (T) - the time taken to produce one wave.

Question 6

What is the equation linking the period and frequency of a wave?

Answer 6

period = 1/frequency

T = 1/f

Question 7

Describe how you could set up an experiment to measure the speed of sound

Answer 7

1. Connect a loudspeaker to signal generator which produces short pulses of sound
2. Place two microphones near to the loudspeaker seperated by a short distance which is measured.
3. Connect each microphone to the input of a dual beam oscilloscope.
4. Use the oscilloscope to measure the time taken for the sound to reach each microscope.
5. You can use the equation speed = distance travelled/time taken to calculate the speed of the sound waves produced.
   NB remember to convert distance into metres and sound into seconds.
   Your answer should come to 330m/s.

Question 8

What are electomagnetic waves?

Answer 8

They are transverse waves that transfer energy from the source of a wave. There are different types of electromagnetic waves and they have a wavelength from about 1 x 10 -11m to about 1km

Question 9

Identify some of the common properties of electromagnetic waves

Answer 9

1. They are transverse waves
2. They transfer energy from one place to another
3. They obey the wave equation v= fλ
4. They can travel through a vacuum
5. They travel through a vacuum at a speed of 300000000m/s ( 3 x 10 8)

Question 10

Identify some of the common electromagnetic waves in order of wavelength shortest to longest

Answer 10

1. Gamma rays
2. X Rays
3. Ultra violet
4. Visible spectrum
5. Infra red
6. Microwaves
7. Radio waves

Question 11

Explain refraction.

Answer 11

Refraction occurs when wavelengths pass from one medium to another and change direction. Different wavelengths refract at different angles. This can cause interesting effects such as a spoon in water appearing to disconnect and light refracting into it’s spectrum colours as it passes through raindrops to give a rainbow.

Question 12

Explain how the different wavelengths of visible light behave differently when they are incident on different surfaces?

Answer 12

1. A red shirt appears to be red because the material reflect red light. All of the other wavelengths are absorbed.
2. Materials which appear white reflect all of the visible spectrum of wavelengths.
3. Black surfaces absorb all of the visible spectrum of wavelengths.

Question 13

A polished metal surface reflects most electromagnetic waves, which waves can pass through think metal?

Answer 13

X Rays and gamma rays

Question 14

Describe how a microwave oven cooks a potato?

Answer 14

The wavelengths of the microwaves emitted by the oven are carefully chosen so that the water molecules in the potato absorb them, heating the potato and cooking it.

Question 15

What is the angle of incidence?

Answer 15

It is the angle between the incident ray and the normal.

Question 16

What is the angle of refraction?

Answer 16

The angle between the refracted ray and the normal.

Question 17

Describe and explain what happens when light passes through a glass block.

Answer 17

1. When the light enters the block it changes direction towards the normal because light travels more slowly in glass than it does in air.
2. When the light leaves the glass it changes direction away from the normal because the light travels faster in air than it does through glass.
3. This is called refraction.
4. The light appears to leave the glass in a different position

Question 18

Describe and explain refraction in water waves.

Answer 18

Refraction can occur in water waves when they move from deep water to shallow water.
If the shallow water is angled then the waves slow down, become shorter in wavelength and change direction.

Question 19

Describe how radio waves are transmitted.

Answer 19

1. A high frequency alternating current is supplied to the transmitting aerial which makes electrons oscillate up and down the aerial.
2. A transverse electromagnetic wave is emitted. This wave transfers energy in oscillating electric and magnetic fields. It is transverse because the oscillations are at right angles to the direction of energy transfer.
3. The electromagnetic wave reaches the receiving aerial. The electric and magnetic fields cause electrons to oscillate up and down the receiving aerial. This induces a current in an electrical circuit.
   The alternating current has the same frequency as the radio wave itself.

Question 20

Identify 2 practical uses of radio waves.

Answer 20

Radio waves carry the information that we see on TV as well as what we hear on a radio.

Question 21

Identify 3 practical uses of microwaves.

Answer 21

1. Used in the home to cook food quickly.
2. Used in satellite communications because they pass easily through the earths atmosphere.
3. Used in mobile phone networks.

Question 22

Identify some practical uses of infrared waves.

Answer 22

1. Used to send signals by remote control to TV’s.
2. Ovens use infrared radiation to cook food.
3. Electric heaters use infrared radiation to provide warmth.
4. Infrared cameras allow night photography.
5. Infra red pulses used in fibre optic communications.

Question 23

Identify some practical uses of light waves.

Answer 23

1. We use light waves all the time so that we can see things.
2. Light pulses are used in fibre optic communications.
3. Lasers which emit high energy visible light are used in surgery.

Question 24

Identify some practical uses of ultraviolet waves.

Answer 24

1. Some substances absorb the energy from ultra violet radiation and emit it as visible light called fluorescence. This can be used in the security industry.
2. Some types of energy efficient lamps.

Question 25

Identify some practical uses of X rays waves.

Answer 25

1. X rays can be used to provide medical images as bones teeth and diseased tissue absorb them, making them stand out on an image.
2. X rays along with gamma rays can be used to to kill cancer cells in radiotherapy treatment.

Question 26

Identify hazards caused by electromagnetic rays.

Answer 26

1. The higher the frequency of the electromagnetic ray the more damage it is likely to do to the body.
2. Ultraviolet, x -rays and gamma rays all cause mutations to cells of the body which can cause cancer.
3. Ultraviolet rays from the sun cause the skin to age prematurely.
4. X Rays and gamma rays are ionising radiations, the effect of a dose of radiation is measured in sieverts.

Question 27

Explain how X rays cab be used to show a broken bone.

Answer 27

When X rays enter the body they are reflected by the soft tissue and absorbed by the bones.
A picture is then taken which shows the bones as light areas and the soft tissues as dark
Abnormalities can be identified from the picture.