Young's Double Slit Experiment: Practice Problem & Solution

Short Solution (Best for NEET):

To solve this problem, we apply the core principles of Young's Double Slit Experiment. Understanding the underlying formula is key to arriving at the correct answer below:

Fringe width is given by $beta = frac{lambda D}{d}$. When $D' = 2D$ and $d' = d/2$, the new fringe width is $beta' = frac{lambda (2D)}{(d/2)} = 4 frac{lambda D}{d} = 4beta$. It becomes four times the original.