Sec 4 Physics General Properties of Waves topical questions

Define amplitude, wavelength, period and frequency of a wave, stating the unit of each.

A wave has frequency 12 Hz and wavelength 0.25 m.

1. (a)Calculate the speed of the wave.[2]
2. (b)State the period of the wave.[1]

Classify each wave as transverse or longitudinal: sound in air, wave on a violin string, ultrasound in tissue, light from a lamp.

A water wave is described by two graphs: a displacement–distance graph with crests 1.6 m apart and amplitude 0.30 m; a displacement–time graph with peaks every 2.0 s.

1. (a)State the wavelength, amplitude and period.[3]
2. (b)Calculate the frequency and speed.[3]

A person claps in front of a cliff and hears the echo 0.90 s later. Sound travels at 340 m/s.

1. (a)Explain why the time must be halved to find the distance.[2]
2. (b)Calculate the distance to the cliff.[2]
3. (c)State one use of this echo technique.[1]

A loudspeaker produces a 512 Hz note in air (speed 340 m/s). The note passes from warm air (340 m/s) into cold air where sound travels at 330 m/s.

1. (a)Calculate the wavelength in the warm air.[2]
2. (b)State what happens to the frequency in the cold air, with a reason.[2]
3. (c)Calculate the new wavelength in the cold air.[2]

A dolphin emits an ultrasound click of frequency 120 kHz towards a school of fish 90 m away and hears the echo. Sound travels at 1500 m/s in sea water.

1. (a)Calculate the time before the echo returns.[2]
2. (b)Calculate the wavelength of the click in the water.[2]
3. (c)State why dolphins use ultrasound rather than low-frequency sound for detecting small fish.[2]

A long spring lies stretched on the floor. A student generates (a) a sideways flick pulse and (b) a push-pull pulse along the spring. Describe each pulse and classify both waves.

A student strikes a tuning fork of frequency 340 Hz and holds it over a tall measuring cylinder of water; sound in air travels at 340 m/s.

1. (a)Calculate the wavelength of the note.[2]
2. (b)The fork is struck harder. State the effect on the amplitude, loudness, frequency and pitch of the note.[3]
3. (c)Explain why the sound is quieter when the fork is touched against the rim of the cylinder.[2]

A ship’s echo sounder emits 30 ultrasound pulses per second, each of frequency 60 kHz. Pulses return from the sea bed 0.25 s after each emission; sound in sea water travels at 1500 m/s.

1. (a)Calculate the depth of the sea bed.[2]
2. (b)Calculate the wavelength of the pulses in the water.[2]
3. (c)Explain one advantage of using pulses (rather than a continuous note) for depth finding.[2]
4. (d)The sea bed rises. State and explain what happens to the echo time.[2]

A student sets two loudspeakers 2.0 m apart to emit the same 850 Hz note (speed of sound 340 m/s) and walks slowly between them. She notices places where the sound is loud and places where it is quiet.

1. (a)Calculate the wavelength of the note.[2]
2. (b)Explain, using wave ideas, why loud and quiet spots alternate along her path.[4]
3. (c)State what happens to the spacing of the quiet spots if the frequency is raised to 1700 Hz.[2]

An ultrasonic scanner sends short pulses into the body. Pulses reflect from the surface of an organ 4.5 cm below the skin and from its far wall 2.0 cm deeper. Sound travels at 1500 m/s in tissue. The display maps echo time to depth.

1. (a)Calculate the time after transmission at which each echo returns to the probe.[4]
2. (b)Explain why the display shows the organ’s thickness correctly without the operator dividing by two.[2]
3. (c)State one reason the scanner uses pulses rather than a continuous signal.[2]