Question

Two sinusoidal plane waves same frequency having intensities $I_0$ and $4I_0$ are travelling in same direction. The resultant intensity at a point at which waves meet with a phase difference of zero radian is

• A. $I_0$
• B. $5I_0$
• C. $9I_0$
• D. $3I_0$

Answer 1

Answer: (C)

$9I_0$

Let, $I_1=I_0$ and $I_2=4I_0$

Resultant intensity, $I=I_1+I_2+2\sqrt{I_1{I}_2}cos\varphi$

$=I_0+4I_0+2\sqrt{I_{0}4I_0}cos{0}^{\circ }=9I_0$