Two beams of light having intensities I and 4I interfere to produce a fringe pattern on a screen. The phase difference between the beams is π2 at point A and 2π at point B. Then the difference between the resultant intensities at B and A will be
A
4I
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B
3I
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C
I
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D
5I
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Solution
The correct option is A4I Resultant amplitude of interference A=√A21+A22+2A1A2cosϕ
Intensity I∝A2 ∴ resultant intensity is given by If=I1+I2+2√I1I2cosϕ
where ϕ is the phase difference between the two waves at the point.
At point A, IA=I+4I+2√I×4I×cosπ2 =5I
At point B, IA=I+4I+2√I×4I×cos2π =9I