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
Correct answer
Explanation
The correct answer is B, light travels much faster than sound. The flash and the clap are produced at the same instant by the same discharge. Light covers about three lakh kilometres in one second, so it reaches the observer almost immediately, while sound in air covers only about 340 metres in a second and takes roughly three seconds for each kilometre. The gap between seeing and hearing is therefore a direct measure of distance.
Option A reverses the true order and would make thunder arrive first, which never happens. Option C is wrong because equal speeds would make the flash and the clap arrive together, with no gap at all. Option D confuses brightness with speed; the flash is indeed very bright, but intensity has nothing to do with why it arrives earlier, and even a faint flash would still be seen before the sound was heard.
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 →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
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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.
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 →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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