Waves

Question 1

What are waves?

Answer 1

Waves can be described as oscillations, or vibrations, about a rest position. All waves transfer energy but they do not transfer matter.

Question 2

Parts of a wave

Answer 2

Waves are described using the following terms:

Rest position – the undisturbed position of particles or fields when they are not vibrating.
Displacement – the distance that a certain point in the medium has moved from its rest position.
Peak – the number of waves passing a point each second. The highest point above the rest position.
Trough – the lowest point below the rest position.

Amplitude – the maximum displacement of a point of a wave from its rest position.

Wavelength – distance covered by a full cycle of the wave. Usually measured from peak to peak, or trough to trough.

Time period – the time taken for a full cycle of the wave. Usually measured from peak to peak, or trough to trough.
Frequency – the number of waves passing a point each second

Question 3

Longitudinal waves

Answer 3

Vibrations are parallel to direction of wave travel. Examples include sound waves, Ultrasound waves and seismic P waves.

Question 4

Transverse waves

Answer 4

Vibrations are at right angles to the direction of wave travel. Examples include ripples on surface of water, vibrations on a guitar string, mexican wave, EM waves and Seismic S waves.

Question 5

Time period calculation

Answer 5

Time period = 1
———-
Frequency

Question 6

Wave speed Calculation

Answer 6

Wave speed = frequency x Wavelength

V = Fx λ

Question 7

Speed of sound calculation

Answer 7

(wave speed is measured in m/s, distance ((X)) is measured in Metres and time (((T))) is measured in seconds)

Speed = distance
Time

v = X
—-
T

Question 8

Ripple tank experiment Method

Answer 8

1. Set up the ripple tank with about 5 cm depth of water.
2. Adjust the height of the wooden rod so that it just touches the surface of the water.
3. Switch on the lamp and motor and adjust until low frequency waves can be clearly observed.
4. Measure the length of a number of waves then divide by the number of waves to record wavelength. It may be more practical to take a photograph of the card with the ruler and take your measurements from the still picture.
5. Count the number of waves passing a point in ten seconds then divide by ten
   to record frequency.
6. Calculate the speed of the waves using: wave speed = frequency × wavelength.

Question 9

Speed of sound through air

Answer 9

330 m/s. Sound cannot travel through a vaccum as there are no particles to carry the vibrations

Question 10

Ultrasound

Answer 10

Higher frequency than the human ear can detect (above 20,000 Hertz)