Question

Two sinusoidal waves of intensity $I$ having same frequency and same amplitude interferes constructively at a point. The resultant intensity at a point will be

• A. $I$
• B. $2I$
• C. $4I$
• D. $8I$

Answer 1

Answer: (C)

$4I$

Answer 2

The resultant intensity is given by $I_{R}=I_{1}+I_{2}+2\sqrt{I_{1}I_{2}} cos\phi=1$ For constructive interference, cos$\phi = 1$ $\therefore\, I_{R}=I_{1}+I_{2}+2\sqrt{I_{1}I_{2}}$ or $\, I_{R}=4I\quad\left(Given I_{1}=I_{2}=I\right)$