Question

If the source of light used in a Young's double slit experiment is changed from red to violet :

• A. the fringes will become brighter.
• B. consecutive fringe lines will come closer.
• C. the intensity of minima will increase.
• D. the central bright fringe will become a dark fringe.

Hint:

Since $\beta \propto \lambda$, Red light produces the widest fringes and Violet produces the narrowest fringes in the visible spectrum.

Answer 1

The Correct Option is B

Step 1: Use the fringe width formula: $\beta = \frac{\lambda D}{d}$.
Step 2: Recall that wavelength $\lambda_{red}>\lambda_{violet}$.
Step 3: Since fringe width $\beta$ is directly proportional to $\lambda$, a decrease in wavelength (red to violet) results in a decrease in fringe width. Therefore, the fringes come closer together.