Chapter 11 Waves and 12 Sound MCQ

A wave transfers

• molecules

• energy

• matter

• force

Answer explanation

Waves transfer energy without transferring matter.

When a transverse wave passes, the particles of the medium oscillate

• in an up and down motion.

• in a left and right motion.

• parallel to the direction of the wave travel.

• perpendicular to the direction of the wave travel.

Answer explanation

A transverse wave has a direction of vibration that is perpendicular to the direction of wave travel.

Which one of the following is an example of longitudinal waves?

• Waves in a ripple tank

• Light waves in air

• A vibrating guitar string

• Sound waves produced by a vibrating guitar string

Answer explanation

Some examples of longitudinal waves are sound waves, certain waves of an earthquake (seismic P-waves) and ultrasound waves.

A wave generator of frequency 3 Hz produces water waves in a ripple tank. Which of the following values of wavelength and speed are possible?

• Wavelength: 3 cm

  Speed: 1 cm/s

• Wavelength: 15 cm

  Speed: 5 cm/s

• Wavelength: 3 cm

  Speed: 6 cm/s

• Wavelength: 4 cm

  Speed: 12 cm/s

Answer explanation

v = fλ

f = v/λ = 12/4 = 3 Hz

The diagram shows a rope wave with two points, X and Y, marked. The wave is moving to the right as shown. What will happen next?

• X wil move up

• X will move to the right

• Y will move up

• Y will move down

Answer explanation

The wave movement is always confusing to students. Students fail to see that the wave motion is caused by the perpendicular movement of the particles along the wave. The following illustration shows the dotted wave as the position of the wave at the next moment. X' and Y' are the new positions of particle X and particle Y respectively.

From the illustration, both X and Y move downward as shown by the positions of X' and Y'.

The diagram illustrates plane waves travelling across two different terrains. How do the frequency and speed of the waves change when they travel from terrain A to terrain B?

• Frequency: no change

  Speed: increase

• Frequency: no change

  Speed: decrease

• Frequency: increase

  Speed: increase

• Frequency: increase

  Speed: decrease

Answer explanation

The frequency of a wave is determined by the source. It does not change with a change in medium. Based on v = fλ, when the wavelength decreases (with the frequency constant) the speed of the wave must decrease.

Which of the following shows the correct wave terms for P and Q?

• P: amplitude

  Q: period

• P: amplitude

  Q: wavelength

• P: half the amplitude

  Q: period

• P: half the amplitude

  Q: wavelength

Answer explanation

Amplitude is the maximum displacement of a wave measured from the equilibrium position. The horizontal axis is labelled as time. The magnitude of Q therefore represents the time taken for one oscillation which is the period of the wave.

Which of the following action(s) could change the wavelength of the ripples made in a ripple tank?

(1) change the water to another type of liquid

(2) increase the frequency of the dipper

(3) change the depth of the water

• (3) only

• (1) and (2) only

• (1) and (3) only

• (1), (2) and (3)

Answer explanation

When the wave travels in a different medium, the speed of the wave will change. Based on v = fλ, when the frequency is kept constant and the speed of the wave change, the wavelength of the wave will change as well. Choice (1) and choice (3) are examples of medium change.

When the frequency of the source changes without changing the medium, the speed of the wave will remain constant. Based on v = fλ, when the speed is kept constant and the frequency of the wave change, the wavelength of the wave will change as well. Choice (2) will therefore cause the wavelength of a wave to change.

A series of compressions and rarefactions of a sound wave is shown below. Given that the sound wave has a frequency of 1600 Hz and a speed of 320 m/s, calculate the distance between P and Q.

• 0.3 m

• 0.4 m

• 0.6 m

• 0.8 m

Answer explanation

v = fλ

320 = 1600λ

λ = 0.2 m

There are three wavelengths from P to Q (one wavelength is the distance from a compression to the adjacent compression).

Distance between P and Q = 3 × 0.2 = 0.6 m

The time taken for one oscillation made in a sound wave is 2.0 ms. Calculate the frequency of the sound wave given that the speed of sound in air is 300 m/s.

• 50 Hz

• 150 Hz

• 500 Hz

• 150 000 Hz

Answer explanation

Period = 2.0 ms = 0.002 s

Frequency = 1/period = 1/0.002 = 500 Hz

Note that the speed of sound of 300 m/s is extra information given.