Properties of Waves
14 Grade 10 Physics questions on Properties of Waves, with worked marking schemes. 14 questions are available on this topic in full.
Question 1
1 markWater waves travel across a pond towards the bank. A dry leaf floating on the water moves up and down as the waves pass beneath it, but it does not move towards the bank. This observation shows that the waves
A. lose all their energy before they reach the bank
B. transfer energy from place to place without carrying the water along with them
C. are longitudinal, because the leaf moves up and down
D. carry the water along with them as they travel
(1 mark)
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1 markA learner at a school near Lake Naivasha watches water waves passing a reed stem. The waves have a frequency of 4 Hz and a wavelength of 0.5 m. The speed of the waves is
A. 2.0 m/s
B. 0.125 m/s
C. 4.5 m/s
D. 8.0 m/s
(1 mark)
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3 marksA fishing boat on Lake Victoria uses an echo sounder. A pulse of sound sent vertically downwards is received back 0.08 s later. Taking the speed of sound in water as 1500 m/s, determine the depth of the water below the boat.
(3 marks)
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1 markWhich one of the following is a longitudinal wave?
A. Sound from a school bell travelling through air
B. Light from a torch
C. Ripples on the surface of a dam
D. Radio waves from an FM station
(1 mark)
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1 markA learner plucks the same string of a nyatiti more strongly, so that the amplitude of the sound wave produced increases while its frequency stays the same. The note produced will be
A. louder but of the same pitch
B. higher in pitch and of the same loudness
C. of the same loudness but higher in pitch
D. lower in pitch and louder
(1 mark)
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4 marksTwo loudspeakers placed a few metres apart at a school prize-giving are fed with the same steady note. As a learner walks slowly along a line in front of them, she notices positions where the note is very loud and positions where it is very faint. Explain these observations.
(4 marks)
Marking scheme
Sound waves from the two loudspeakers overlap (superpose) in the region in front of them (1 mark). At some positions the two waves arrive in phase, the path difference being a whole number of wavelengths (1 mark). There they reinforce each other, that is constructive interference, and a loud sound is heard (1 mark). At other positions the waves arrive out of phase, the path difference being an odd number of half wavelengths, so they cancel, that is destructive interference, and a faint sound is heard (1 mark).
Question 7
1 markIn a train of water waves, the distance from a crest to the next trough is 0.3 m. The wavelength of the waves is
A. 0.6 m
B. 1.2 m
C. 0.15 m
D. 0.3 m
(1 mark)
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2 marksDistinguish between the frequency and the period of a wave.
(2 marks)
Marking scheme
Frequency is the number of complete waves (oscillations) produced by the source, or passing a fixed point, in one second (1 mark). Period is the time taken for one complete wave (oscillation) to pass a fixed point, or for the source to make one complete oscillation (1 mark). [The relation T = 1/f alone earns nothing unless both quantities are defined.]
Question 9
1 markAn electric bell is set ringing inside a glass jar and the air in the jar is slowly pumped out. The sound heard outside becomes fainter and finally dies away, although the hammer is still seen striking the gong. This shows that
A. light needs a material medium to travel through, while sound does not
B. sound needs a material medium to travel through, while light does not
C. the bell stops vibrating once the air has been removed
D. sound travels faster in a vacuum than it does in air
(1 mark)
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1 markStraight water waves in a ripple tank pass through a gap in a barrier. When the gap is made narrower, the waves beyond the barrier
A. spread out more into the region behind the barrier
B. travel faster than before
C. have a shorter wavelength than before
D. have a higher frequency than before
(1 mark)
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4 marksA learner standing behind a tall building at a bus stage in Nakuru can clearly hear the hooter of a matatu on the far side of the building, but cannot see the matatu at all. Explain this observation.
(4 marks)
Marking scheme
Waves bend (spread) round the edges of an obstacle; this is diffraction (1 mark). The spreading is large only when the wavelength is comparable with the size of the obstacle or gap (1 mark). Sound waves have wavelengths of the order of a metre, comparable with the building, so they are diffracted strongly and reach the learner's ears (1 mark). Light has an extremely short wavelength compared with the building, so it is diffracted only very slightly and travels on in straight lines; no light from the matatu reaches the learner's eyes (1 mark).
Question 12
4 marksA farmer in Kitale sees a flash of lightning and hears the thunder 6 seconds later. Explain why the flash is seen before the thunder is heard, and determine how far away the lightning was. (Speed of sound in air = 340 m/s)
(4 marks)
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3 marksWaves on Lake Baringo pass a fisherman's boat. Successive crests are 6 m apart and 20 crests pass the boat in 40 seconds. Determine the speed of the waves.
(3 marks)
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5 marksWater waves travel from a deep region of a ripple tank into a shallow region.
(a) State what happens to the speed, the wavelength and the frequency of the waves.
(b) Explain the change in wavelength and the behaviour of the frequency.
(5 marks)
Marking scheme
(a) Speed decreases (1 mark). Wavelength decreases (1 mark). Frequency remains constant (1 mark). (b) The frequency is fixed by the vibrating source (dipper), which is not altered by the change of depth (1 mark). Since v = f x wavelength and f is constant, wavelength is proportional to speed, so a smaller speed gives a smaller wavelength (1 mark).
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