Question

In case of interference of two waves each of intensity $I_{0}$, the intensity at a point of constructive interference will be

• A. $4 I_{0}$ for coherent source
• B. $2 I_{0}$ for coherent source
• C. $4 I_{0}$ for incoherent source
• D. $2 I_{0}$ for incoherent source

Answer 1

Answer: (A), (D)

When the sources are coherent,
$R^{2}=a^{2}+b^{2}+2 a b \cos \phi$
for constructive interference, $\phi = 0$
$\therefore I=I_{0}+I_{0}+2 \sqrt{I_{0} I_{0}} \cos 0^{\circ}=4 I_{0}$
When the sources are incoherent, intensities just add
$I=I_{0}+I_{0}=2 I_{0}$