Which of the followings is correct for waves?
a. One wave can cancel another wave so that no amplitude remains at certain points.
b. While you are at rest, a car moves toward you while it is making noise. The speed of this sound wave is greater than when the car is stationary.
c. Without exception, any radio wave travels faster than any sound wave.
d. X-rays travel faster in vacuum than in air.
a,c,d
To determine which of the statements is correct for waves, we can analyze each statement individually.
a. One wave can cancel another wave so that no amplitude remains at certain points.
This statement is correct and relates to the concept of wave interference. When two waves with the same amplitude and opposite phase meet, they can cancel each other out, resulting in no amplitude at certain points. This phenomenon is called destructive interference.
b. While you are at rest, a car moves toward you while it is making noise. The speed of this sound wave is greater than when the car is stationary.
This statement is incorrect. The speed of sound in a medium, such as air, depends on the properties of that medium and is independent of the motion of the source or observer. The speed of sound remains the same regardless of whether the car is stationary or moving towards you.
c. Without exception, any radio wave travels faster than any sound wave.
This statement is correct. Radio waves are a type of electromagnetic wave, and electromagnetic waves, including radio waves, travel at the speed of light in a vacuum, which is approximately 3 x 10^8 meters per second. On the other hand, sound waves are mechanical waves that require a medium (like air, water, or solid) to propagate and are much slower than electromagnetic waves.
d. X-rays travel faster in a vacuum than in air.
This statement is incorrect. The speed of electromagnetic waves, including X-rays, is constant and does not depend on the medium in which they travel. In both vacuum and air, X-rays travel at the speed of light.