Which one of the following statements about the speed of sound waves is not correct?
- A.The speed of sound waves in steel is higher than that in water.
- B.The speed of sound waves in air decreases with increase in temperature.
- C.The speed of sound waves in air increases with increase in temperature.
- D.The speed of sound waves in water is higher than that in air.
Correct answer
Explanation
The correct answer is B. The speed of sound in air increases, not decreases, as temperature rises, so statement B is the incorrect one.
Sound in a gas travels faster when the gas is warmer, because its molecules move faster and pass the vibration on more quickly. The speed is proportional to the square root of the absolute temperature, and in air it rises by about 0.6 m/s for every 1 °C. It is about 331 m/s at 0 °C and about 343 m/s at 20 °C. Sound also travels faster in liquids than in gases and fastest in solids, because their particles are more tightly bound: roughly 1,500 m/s in water and about 5,000 to 6,000 m/s in steel.
A is a correct statement: sound is several times faster in steel than in water. C is a correct statement and is simply the opposite of B. D is a correct statement: sound in water is more than four times as fast as in air.
Exam tip: speed of sound is fastest in solids, then liquids, then gases; in air it grows with temperature, about 0.6 m/s per °C.
Practice Questions
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- A.perpendicular to each other.
- B.parallel to each other.
- C.anti-parallel to each other.
- D.equal in magnitude.
Show answer
Work is negative when the force acts opposite to the displacement, because the angle between them is then 180°. Work done is W = F S cos θ, where θ is the angle between the force and the displacement.
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- B.Satellite is kept in orbit by retro-rocket and solar energy keeps it moving around the Earth.
- C.Satellite requires energy from solar panels and solid fuels for orbiting.
- D.Satellite does not require any energy for orbiting.
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- A.Frictional force
- B.Electric force
- C.Gravitational force
- D.Spring force
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- A.electrical signals to sound waves
- B.sound waves to electrical signals
- C.microwaves to sound waves
- D.sound waves to microwaves
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- A.bending towards the normal
- B.bending away from the normal
- C.propagating in straight line
- D.reflected towards the opposite direction
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