Question

Two waves of intensity $I$ undergo interference. The maximum intensity obtained is:

• A. $\frac{I}{2}$
• B. $I$
• C. $2I$
• D. $4I$

Answer 1

Answer: (D)

When two interfering waves meet in the same phase, resultant intensity is maximum. The resultant intensity due to two waves
$I_1$ and $I_2$
and having phase difference
$\varphi$ between them is given by
$I=I_1+I_2+2\sqrt{I_1{I}_2}\cos \varphi$
For maximum intensity, $\varphi =0$
$\therefore$ $I_{\max }={(\sqrt{I_1}+\sqrt{I_2})}^2$
Given, $I_1=I_2=I$
$\therefore$ $I_{\max }={(\sqrt{I}+\sqrt{I})}^2=4I$
Maximum intensity is also known as constructive interference.