A sound wave has a frequency of 1 kHz and wavelength 50 cm. How long will it take to travel 1 km?
- A.5 s
- B.4 s
- C.3 s
- D.2 s
Correct answer
Explanation
The correct answer is D, 2 s. Convert the units first: 1 kilohertz is 1000 hertz and 50 centimetres is 0.5 metre. The speed is frequency multiplied by wavelength, that is 1000 multiplied by 0.5, which gives 500 metres per second. Time equals distance divided by speed, so 1000 metres divided by 500 metres per second gives 2 seconds.
Option A, 5 s, would follow from using a speed of 200 metres per second. Option B, 4 s, corresponds to a speed of 250 metres per second, which arises if the wavelength is halved by mistake. Option C, 3 s, is close to the time sound actually takes to cover a kilometre in ordinary air, about 340 metres per second, and is the trap for candidates who use the remembered speed of sound instead of the speed calculated from the data given.
Read the full article: Sound and Waves: Properties, Speed and PYQs
Practice Questions
View allThe frequency of a sound wave is 50 Hz and its wavelength is 4 m. What is the distance travelled by the sound wave in 3 s?
- A.100 m
- B.600 m
- C.200 m
- D.300 m
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The speed of a wave is the product of its frequency and its wavelength, so the speed here is 50 hertz multiplied by 4 metres, that is 200 metres per second.
Read the full explanation →The brain interprets the frequency of an emitted sound called -
- A.Wavelength
- B.Wave velocity
- C.Pitch
- D.Oscillation
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Pitch is the characteristic of a sound by which the brain judges it as shrill or flat, and it is decided by the frequency of the wave.
Read the full explanation →The loudness of sound depends upon the
- A.velocity of sound waves in the medium.
- B.amplitude of the sound waves.
- C.frequency of the sound waves.
- D.frequency and velocity of the sound waves.
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Amplitude is the maximum displacement of a particle of the medium from its rest position, and the energy carried by a wave increases with the square of the amplitude.
Read the full explanation →The flash of lightning is seen before the thunderstorm is heard. It verifies that
- A.sound travels much faster than light
- B.light travels much faster than sound
- C.light and sound both travel with same speed
- D.intensity of flash of lightning is very high during thunderstorm
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The flash and the clap are produced at the same instant by the same discharge.
Read the full explanation →Sound waves are:
- A.Transverse electromagnetic waves
- B.Longitudinal mechanical waves
- C.Transverse mechanical waves only in solids
- D.Waves that need no medium to travel
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In a sound wave the particles of the medium vibrate back and forth along the same line in which the wave is travelling, producing regions where they crowd together, called compressions, and regions where they spread apart, called rarefactions.
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