Question

In biprism experiment, the distance of the 20th bright band from the central bright band is 1.2 cm. Without changing the experimental set-up, the distance of the 30th bright band from the central bright band will be:

• A. 0.6 cm
• B. 0.8 cm
• C. 1.2 cm
• D. 1.8 cm

Hint:

Fringe width remains constant in a given experimental setup. The position of bright or dark fringes is proportional to fringe order.

Answer 1

The Correct Option is D

Step 1: In Young’s double-slit experiment, the distance of the \( n \)-th bright fringe from the central fringe is given by: \[ x_n = n \lambda D / d. \] Since the setup remains unchanged, the ratio of fringe positions is: \[ \frac{x_{30}}{x_{20}} = \frac{30}{20} = \frac{3}{2}. \] Step 2: Given \( x_{20} = 1.2 \) cm, \[ x_{30} = \frac{3}{2} \times 1.2 = 1.8 { cm}. \] \bigskip