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| Waves and optics |
1. Can two independent sources of light produce interference?
Ans: Two independent sources cannot be coherent because:
i) Light is emitted by emitted by individual atoms and not by the bulk of matter acting as a whole.
ii) Even a tiniest source consists of millions of atom, and emission of light by them takes place independently.
iii) Even an atom emits an unbroken wave of above 10-8 second due to its transition from a higher energy state to a lower energy state.
As a result of above factors, the phase difference between two independent light sources changes after very 10-8 second. So, the position of maxima and minima of intensity will change about 108 times in one seconds. Such rapid changes cannot be seen by our eyues and almost a uniform illumination on the screen is observed. Hence, two independent light sources cannot produce a sustained interference pattern.
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