Topic 6: Waves

Question 1

Describe the method of the ripple tank practical

Answer 1

Frequency:
- put a stop clock on the screen
- use a digital camera to record the waves passing a point
- replay in slow motion and count the number of waves passing a point per second
(Or read frequency off the oscillator)

Wavelength:
- place a metre rule at the side of the screen perpendicular to the wave fronts
- take a photograph of the shadow on the screen
- use the metre rule to measure the distance between two wave fronts
- measure 10 waves then divide by 10 to find one wave

Wave speed = frequency x wavelength

Question 2

What is the equation find the period of a wave?

Answer 2

Period = 1/frequency

Question 3

What is period and frequency measured in?

Answer 3

• period (T) is measured in seconds (s)
• frequency (F) is measured in hertz (Hz)

Question 4

Define wave speed

Answer 4

The speed at which the energy is transferred (or the wave moves) through the medium

Question 5

What is the equation that links wave speed, frequency and wavelength? (Give units)

Answer 5

Wave speed (m/s) = frequency (Hz) x wavelength (m)

Question 6

What is the amplitude of a wave?

Answer 6

The maximum displacement of a point on a wave away from its undisturbed position

Question 7

What is the wavelength of a wave?

Answer 7

The distance from a point on one wave to the equivalent point on the adjacent wave

Question 8

What is the frequency of a wave?

Answer 8

The number of waves passing a point each second

Question 9

Explain why for both ripples on a water surface and sound waves in air, it is the wave and not the water or air itself that travels

Answer 9

The wave is moving not the median (like a Mexican wave - the people don’t move but the wave does)

Question 10

Describe the differences between transverse and longitudinal waves in terms of the structure

Answer 10

Transverse waves - peaks and troughs

Longitudinal waves - compressions and rarefactions

Question 11

Describe the differences between transverse and longitudinal waves in terms of the vibration

Answer 11

Transverse waves - 90 degrees to direction of energy transfer

Longitudinal waves - parallel to direction of energy transfer

Question 12

Describe the differences between transverse and longitudinal waves in terms of vacuum

Answer 12

Transverse waves - only electromagnetic waves can travel in vacuum

Longitudinal waves - cannot travel in a vacuum

Question 13

Describe the differences between transverse and longitudinal waves in terms of the material

Answer 13

Transverse waves - can move in liquids and solids, but not in gases

Longitudinal waves - can move in gas, liquids and solids

Question 14

Describe the differences between transverse and longitudinal waves in terms of density

Answer 14

Transverse waves - constant density

Longitudinal waves - changes density

Question 15

Describe the differences between transverse and longitudinal waves in terms of pressure

Answer 15

Transverse waves - pressure is constant

Longitudinal waves - changes in pressure

Question 16

Describe the differences between transverse and longitudinal waves in terms of the speed of wave

Answer 16

Transverse waves - dependant on material it is travelling in

Longitudinal waves - dependant on material it is travelling in

Question 17

What are the two types of waves?

Answer 17

Transverse and longitudinal

Question 18

Give an example of transverse waves

Answer 18

The ripples on a water surface, EM waves, vibration on a guitar string

Question 19

Give an example of longitudinal waves

Answer 19

Sound waves travelling through the air, ultra-sound

Question 20

What are the control variables for the waves on a string practical?

Answer 20

• number of masses as it controls tension of string
• length of string - affects how many waves produced
• type of string - affects how many waves produced

Question 21

Describe the method for the waves on a string practical

Answer 21

1) switch the signal generator and vibration generator on so the string vibrates up and down
2) move the wooden bridge until a clear wave pattern is formed between the wooden bridge and the vibration generator
3) use a metre rule to measure the length of the string between the wooden bridge and the vibration generator
4) record the frequency of the wave from the signal generator
5) record the number of loops in the wave pattern
6) change the frequency on the signal generator until a new wave pattern is formed
7) repeat steps 4-6