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| Doppler Effect in Light |
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| Whenever there is a relative motion between a source of light and the observer, the apparent frequency of light received by the observer is different from the true frequency of light emitted actually from the source of light. |
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| If a source of light emits waves of frequency f and of wavelength l, then the velocity of light would be c = lf. |
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| When the source and the observer approach each other with a velocity v along the direction of propagation of light, then in one second, the two come closer by a distance v. |
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| \ Apparent frequency = number of light waves received per second by the observer. |
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| f|= number of light waves emitted/sec by source + number of light waves contained in a distance v |
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| Clearly f|>f |
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| When the source and the observer move away from each other, then, |
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| When source and the observer approach each other Df is +ve and the apparent frequency fl increases or apparent wavelength decreases. This is 'Blue Shift'. |
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| When the source and the observer recede away from each other, Df is negative and the apparent wavelength increases. This is called the Red shift. |
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