Question

In Young's double slit experiment, if the source of light changes from orange to blue, then

• A. the central bright fringe will become a dark fringe
• B. the distance between consecutive fringes will decrease
• C. the distance between consecutive fringes will increase
• D. the intensity of the minima will increase.

Hint:

Smaller wavelength → smaller fringe width → fringes get closer.

Answer 1

The Correct Option is B

Concept: Fringe width in YDSE: \[ \beta = \frac{\lambda D}{d} \]

Step 1: Fringe width depends directly on wavelength: \[ \beta \propto \lambda \]

Step 2: Blue light has smaller wavelength than orange light: \[ \lambda_{\text{blue}}<\lambda_{\text{orange}} \]

Step 3: \[ \therefore \beta \text{ decreases} \] \[ \Rightarrow \text{fringes come closer} \] Therefore, the distance between consecutive fringes will decrease.