MUS

Question 1

Describe a longitudinal wave in terms of pressure variation and the
displacement of molecules and give examples.

Answer 1

In a longitudinal wave (eg sound, ultrasound, P-waves, etc) oscillations are parallel to the direction of energy transfer. The oscillations of the particles produces small changes in pressure in the medium. A higher density of particles corresponds to a higher pressure, and a lower density corresponds to a lower pressure.

Question 2

Describe a transverse wave and give examples.

Answer 2

A wave (eg EM waves and S-Waves) in which oscillations of particles are perpendicular to the direction of energy transfer.

Question 3

Define amplitude.

Answer 3

The displacement between the resting point of a wave and its peak or trough.

Alternatively, half of the distance between the peak and the trough of a wave.

Amplitude is measured in metres.

Question 4

Define frequency.

Answer 4

The number of times a wave passes a specific point every second, measured in hertz.

Question 5

Define period.

Answer 5

The amount of time it takes for a full wavelength to occur, measured in seconds.

Question 6

Define wavespeed.

Answer 6

The distance travelled by a wave per unit time, measured in metres per second.

Question 7

Define wavelength.

Answer 7

The distance between one point on a wave and the same point on the next wave, measured in metres.

Question 8

Define wavefront.

Answer 8

A surface over which the phase of the wave is constant. In a particular wave front, at a given moment of time, all particles of the medium are undergoing the same motion.

Question 9

Define coherent waves.

Answer 9

A collective of 2 or more waves which have a constant phase difference or no phase difference and the same frequency.

Question 10

Define path difference.

Answer 10

The difference in the distance covered by two waves emitted by two different sources.

Question 11

Define phase difference.

Answer 11

The difference in the phase angle of the two waves emitted from two different sources.

Question 12

Define superposition.

Answer 12

The interaction occurring between two or more waves of the same type overlapping in space.

Question 13

Define interference.

Answer 13

The effect of superposition.

Question 14

Describe how a standing wave is formed.

Answer 14

• A wave travelling through a medium is reflected, resulting in two waves with the same frequency and wavelength travelling in opposite directions
• Superposition occurs
• Constructive interference causes maximum displacement (antinodes)
• Destructive interference causes minimum displacement (nodes)

Question 15

State the equation used when determining the speed of sound.

CPAC 6

Answer 15

v = fλ

Question 16

Describe the method used when determining the speed of sound.

CPAC 6

Answer 16

1. Set the oscilloscope to produce a frequency of 1000Hz.
2. Place the microphone adjacent to or on top of the metre rule.
3. Adjust the distance between the microphone and the speaker until the wave produced by the speaker is in phase with the wave produced on the software received by the microphone.
4. Measure and record the distance between the speaker and the microphone.
5. Repeat Steps 3 and 4 two to three times so that three to four unique values have been measured and recorded.
6. Increase the frequency produced by the frequency produced by the oscilloscope by 1000Hz.
7. Repeat Steps 2 - 6 up to 7000Hz.
8. Calculate the path difference for each frequency by subtracting one measurement of distance from the previous. Calculate an average path difference by dividing the sum of all values by the number of values.
9. Average path difference is equal to the average wavelength.
10. Plot wavelength (y-axis) against time period (x-axis) on a graph.
11. Wave speed (the speed of sound) is the gradient of the line plotted. To calculate it, use the equation Δy/Δx (Δλ/ΔT).

Question 17

State the safety risks and hazards present when determining the speed of sound.

CPAC 6

Answer 17

Hazards:
- Exposure to high frequencies/amplitudes of sound for an extended period of time
- Electric devices
- Heavy speaker

Risks:
- Ear damage
- Electric shock
- Crushing/damaging of body parts

Question 18

State the dependent, independent and controlled variables when determining the speed of sound.

CPAC 6

Answer 18

The independent variable is frequency (f, measured in hertz).

The dependent variable is wavelength (λ, measured in metres).

Controlled variables include:
- Medium used (air)
- Temperature (room temperature, do not open windows or turn on heaters during the investigation)
- Amplitude of sound waves (volume of sound)
- Nearby sources of noise (silence other than the speaker)
- Microphone sensitivity (use the same microphone)
- Person measuring metre rule
- Degree of accuracy of measurements (3 significant figures)

Question 19

State the equipment used when determining the speed of sound.

CPAC 6

Answer 19

• Oscilloscope
• Microphone
• Speaker
• Computer system (to display microphone input/oscilloscope output)
• Insulated wires (to connect devices)
• Metre rule

Question 20

State the potential sources of error when determining the speed of sound.

CPAC 6

Answer 20

• Misreading the metre rule
• Placing the microphone at an incorrect distance from the speaker (either due to unintentional movement or misjudgement of when the two waves on the display are in phase)
• Slight noises could be picked up by the microphone, disrupting the display which would make waves more difficult to interpret
• The speaker producing an incorrect frequency (likely due to being damaged or not being correctly calibrated)
• The temperature of the room may have changed as the investigation progressed