Question

In a double slit experiment, two incoherent sources are placed at the two slits. The intensity of sources at $S_1$ is $I_0$ and that at $S_2$ is $3I_0$. Identity the correct statement.

• A. Destructive interference will result at central position on screen.
• B. The resultant intensity at centre of screen will be $3I_0$.
• C. The resultant intensity at any point on screen will be $4I_0$.
• D. The resultant intensity at any point on screen will be $2I_0$.

Answer 1

The correct option is C The resultant intensity at any point on screen will be $4I_0$.

In case of incoherent sources, we will not get any interference pattern.

The intensity at all points on screen will be uniform.

$\Rightarrow I_R=I_1+I_2$

$\therefore I_R=I_0+3I_0=4I_0$

Hence, $\left(C\right)$ is the correct answer.

Why this question? Note: Two different sources of light are always incoherent despite being identical. It happens due to randomness of electrons in both objects. So, a single source need to be split by using lens or mirror to obtain coherent sources.