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Doppler effect

المؤلف:  Simon Singh

المصدر:  Big Bang

الجزء والصفحة:  p-426

2026-10-25

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Doppler effect The change in wavelength of sound or electromagnetic waves emitted by a moving source. The same effect occurs if it is the observer (not the source) that is moving. Waves are compressed ahead of the source and stretched behind it, producing, for example, the familiar change in the pitch of a siren from high to low as an ambulance passes by at speed. A similar effect causes the redshift in the spectrum of a receding galaxy.