Waves

Question 1

what are the two types of waves

Answer 1

mechanical and electromagnetic

Question 2

what is an example of a transverse wave?

Answer 2

the ripples on a water surface

Question 3

longitudinal waves show areas of what?

Answer 3

compression and rarefraction

Question 4

what type of waves are sound waves travelling through the air.

Answer 4

longitudinal

Question 5

what is the difference between transverse and longitudinal waves?

Answer 5

In longitudinal waves , the vibrations are parallel to the direction of wave travel.

In transverse waves , the vibrations are at right angles to the direction of wave travel.

Question 6

Waves transfer energy without transferring ……………..

Answer 6

Waves transfer energy without transferring matter.

Question 7

Some waves need to travel through a substance, for example……….or…………

Answer 7

for example air or water.

Question 8

what happens when waves travel through a substance

Answer 8

As the wave passes the particles of the substance are disturbed and oscillate (move back and forth).

Once the wave has passed, the particles return to their original positions.

Question 9

Mechanical waves:

Answer 9

sound, water, seismic, waves on springs or ropes

travel through a medium (or substance) that oscillates

An example of energy transfer by mechanical working

Question 10

Electromagnetic waves:

Answer 10

Radio, microwave, IR, light, UV, X Ray, Gamma Ray

These are oscillations in magnetic and electric fields

They do not need a substance.

They can travel through a vacuum, like space.

Responsible for heating by radiation

Question 11

Mechanical waves can travel in two ways:

Answer 11

Longitudinal waves

Transverse waves

Question 12

Wavelength:

Answer 12

This is the distance from a point on one wave to the same point on the next wave. It is measured in metres and has the symbol λ (Greek letter lambda)

Question 13

Amplitude:

Answer 13

the height of the wave from the rest position to a peak or trough. Measured in metres. The more energy a wave has the bigger the amplitude is.

Question 14

Frequency

Answer 14

this is the number of waves passing a point every second and is measured in hertz (Hz).

Question 15

Calculating wave speed:

Answer 15

Wave speed = frequency x wavelength

Question 16

what is wave speed?

Answer 16

The speed of a wave is how far a peak or trough moves every second.

Question 17

period:

Answer 17

period T (seconds) = 1 / frequency (Hz)

Question 18

frequency:

Answer 18

frequency (Hz) = 1 / period (s)

Question 19

what is an echo?

Answer 19

When sound waves hit a smooth, hard surface they are reflected back towards their source. This means you hear an echo a few seconds after you make the original sound.

Question 20

If the distance to the wall and the time delay are measured you can calculate the speed of sound in air using this equation:

Answer 20

speed = distance to object and back (2d) / time delay (t)

Question 21

What will happen to the pitch if the frequency is increased?

Answer 21

It will increase. The higher the frequency, the higher the pitch.

Question 22

Waves Required Practical - ripple tank

Answer 22

1. Set up the ripple tank and switch on both the overhead lamp and the electric motor.
2. Adjust the speed of the motor so that low frequency water waves are produced.
3. Adjust the height of the lamp so that the pattern can be clearly seen on the card on the floor.
4. Place a 30cm ruler at right angles to the waves shown in the pattern on the card. Measure across as many waves as possible then divide that length by the number of waves. This gives the wavelength of the waves.
5. Count the number of waves passing a point in the pattern over 10 seconds. Then divide the number of waves counted by 10. This gives the frequency of the waves.
6. Calculate the speed of the waves using the equation:
   wave speed = frequency x wavelength

Question 23

Waves Required Practical - string

Answer 23

1. Switch on the vibration generator. A clear wave pattern should be seen and the nodes should look like they are stationary.
2. Use a metre ruler to measure across as many half wavelengths as possible (a half wavelength is one loop) record the total length:
3. Divide the total length by the number of half waves - This will give you the length of each half wave
4. Double the length of the half wave to work out the wavelength.
5. Calculate the speed of the wave using the equation:
   wave speed = frequency x wavelength.

Question 24

Bell in a vacuum demo

Answer 24

Sound waves are mechanical so they need a medium (particles) to travel. This means they cannot travel through a vacuum.

When the air is removed from the jar the sound can’t travel from the buzzer to your ear, so you can’t hear it.

Question 25

What happens to a wave when it meets a material depends on the material itself and the wavelength of the wave.

Answer 25

Some, all or none of the wave can be:
Reflected
Refracted
Absorbed
Transmitted

Question 26

What happens when waves hit a barrier straight on?

Answer 26

If they are at a zero angle to the barrier they will be reflected straight back

Question 27

incident ray = ?

Answer 27

reflected ray

Question 28

Refraction

Answer 28

As light travels into a more dense medium (from air to glass) the light ray bends towards the normal line.

Question 29

What is reflection

Answer 29

When light from an object is reflected by a surface, it changes direction.

Question 30

why do waves bend

Answer 30

because they change speed

Question 31

Waves are refracted when they _____ _____.
When waves ____ ____ they bend towards the normal line. This happens when light travels from air to glass or when water waves move from _______ water to _______ water.

When waves ______ _____ they bend away from the normal line. This happens when light travels from glass to air or when water waves move from _______ water to _______ water.

Answer 31

Waves are refracted when they change speed.

When waves slow down they bend towards the normal line. This happens when light travels from air to glass or when water waves move from deep water to shallow water.

When waves speed up they bend away from the normal line. This happens when light travels from glass to air or when water waves move from shallow water to deep water.

Question 32

What happens to the wavefronts during refraction?

Answer 32

When wavefronts cross a boundary at an angle they change speed and direction.

The wavefronts slow down when they cross the barrier so the refracted wavefronts are closer together and at a smaller angle to the boundary than the incident wavefronts.

Question 33

Wavelength changes during refraction

Answer 33

Refracted waves and incident waves have the same frequency but they travel at different speeds so they have different wavelengths.