Question

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 p/2 at point A and p at point B. Then the difference between the resultant intensities at A and B is –

• A. 2I
• B. 4I
• C. 5I
• D. 7I

Answer 1

Answer: (B)

4I

Answer 2

I = I₁ + I₂ + $2\sqrt{I_{1}I_{2}}$cos f

I_A = I + 4I + $2\sqrt{I \times 4I}$ cos $\frac{\pi}{2}$ = 5I

I_B = I + 4I + $2\sqrt{I \times 4I}$ cos p = I

I_A – I_B = 5I – I = 4I