The intensity of light due to (see figure) interference of two waves (1) and (2) which have path difference of λ is: (where I0 = Intensity of each wave)
Answer & explanation
Correct answer: option 4
Path difference is $\lambda$
$\Rightarrow \phi = 2\pi$
$ I = I_0 + I_0 + 2\sqrt{I_0 I_0} cos{2\pi} = 4\ I_0$