Question

Two sinsuoidal waves of intensity I having same frequency and same amplitude interfers constructively at a point. The resultant intensity at a point will be:

• A. I
• B. 2I
• C. 4I
• D. 8I

Answer 1

The correct option is C 4I

For two interfering waves, the resultant intensity is given by:

$I_R=I_1+I_2+2\sqrt{I_1{I}_2}\cos \varphi$

Since frequencies are same, intensity is directly proportional to square of amplitude.

For constructive interference, $\varphi =0$, and with $I_1=I_2=I$, we get $I_R=4I$