Question

If two sources emit light waves of different amplitudes then

• A. brightness of fringes is less.
• B. fringes disappear after short time.
• C. fringe width is less.
• D. there is some intensity of light in the region of destructive interference.

Hint:

Remember that unequal amplitudes lower the overall contrast of an optical pattern but do not change its geometric spacing! The fringe width formula ($\beta = \frac{\lambda D}{d}$) depends only on wavelength and layout dimensions, so it remains completely unchanged.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
Identify the consequence in an interference pattern when the two sources have unequal amplitudes (a₁ ≠ a₂).

Step 2: Key Formula or Approach:
I_min ∝ (a₁ – a₂)². If a₁ ≠ a₂, I_min>0, so dark fringes are not completely black.

Step 3: Detailed Explanation:
Unequal amplitudes mean incomplete destructive interference, leaving residual intensity at minima instead of perfect darkness.

Step 4: Final Answer:
There is some intensity in regions of destructive interference, matching option (D).