2. Wave Speed

Question 1

What is the equation for calculating wave speed?

Answer 1

c = fλ

c = wave speed (m/s)
f = frequency (Hz or s^-1)
λ = wavelength (m)

Question 2

What is the speed of an EM wave in a vacuum?

Answer 2

3.00 x 10^8 m/s

Question 3

Describe the method used to measure the speed of sound

Answer 3

1. Use two microphones in a straight line distance d apart (the microphones should have separate inputs so the signals from each can be recorded separately)
2. Use signal generator to produce sound from the loudspeaker
3. Use computer to record time between first and second microphone picking up the sound
4. This is done by measuring time delay between the first peak of the signal received by each microphone on a graph of voltage against time
5. Use speed = distance / time to measure speed of sound waves

Question 4

Describe the method used to measure the wave speed in water

Answer 4

1. Set up a ripple tank
2. Record the depth of the water in the tank using a ruler
3. Use ripple tank dipper to create vibrations with a regular frequency in the tank
4. Dim main lights in room and turn on strobe light (light that flashes periodically)
5. Increase frequency of strobe light from 0 until waves appear to be standing still (this frequency is the frequency of the water waves)
6. Use ruler on white paper below tank to measure distance between two adjacent peaks (wavelength)
7. Calculate wave speed using the equation c = fλ
8. Repeat experiment with a range of water depths

Question 5

Do waves travel faster in shallow or deep water?

Answer 5

Deep water

Question 6

How can you improve the accuracy of measuring the wavelength in the ripple tank experiment?

Answer 6

Measure distance between several peaks and divide this by number of troughs in between