Dopplers Principle
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-213
2025-11-23
11
When both the sounding body and the ear that hears the sound are stationary, the number of waves that strike the ear per second is the same as the number sent out by the vibrating body; but if either is moving from a position of rest, either toward or away from the other, the number of vibrations that reach the ear per second, and consequently the pitch of the tone heard, are changed.
If N represents the number of vibrations of the sounding body, I the wave length, and d the distance over which the ear moves toward it in one second, then the number of vibrations heard by the ear will be N+ d/L , and the pitch will be raised. The sounding body may itself be moving, or both it and the ear may be moving. If the distance between the bodies is increasing, let d represent the increase per second; the number of vibrations received will be N- d/L and the pitch will be lowered. A good example of this effect is noticed when two trains pass each other while the engine bells are ringing. A man standing by the roadside notices. that the pitch of the horn of an approaching automobile is higher than it is after the machine has passed.
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