Question

State the required conditions for the interference of light. Find the value of maximum resultant intensity of two waves having intensities \( I \) and \( 4I \), when sources are (i) coherent and (ii) non-coherent.

Hint:

In coherent interference, amplitudes add; in non-coherent interference, intensities add.

Answer 1

Conditions for Interference of Light: The sources must be coherent (having a constant phase difference). \item The sources should emit light waves of the same frequency and wavelength.  The sources must have equal or nearly equal intensity for clear visibility. the superposition of waves should occur in the same medium.

Step 1: For coherent sources: \[ I_{\text{max}} = (\sqrt{I} + \sqrt{4I})^2 \] \[ = (1 + 2)^2 I = 9I \] \[ \boxed{9I} \] 

Step 2: For non-coherent sources, the intensities add directly: \[ I_{\text{total}} = I + 4I = 5I \] \[ \boxed{5I} \]