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Two identical light waves traveling along the same direction interfere with a phase difference of δ. The intensity of the combined wave is proportional to

1. cos δ
2. cos(δ/2)
3. cos²(δ/2)
4. cos² δ

Correct answer: cos²(δ/2)

Solution

For two identical waves with phase difference delta, the resultant intensity is I = 4I0 cos^2(delta/2), i.e. proportional to cos^2(delta/2).

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