Question

The fringe width changes from 0.24 mm to 0.3 mm when the screen is moved by 20 cm away from the slits separated by 2 mm. calculate the wavelength of light used.

• A. 400 nm
• B. 500 nm
• C. 600 nm
• D. 700 nm

Answer 1

The correct option is C 600 nm

${\beta }_1=\frac{\lambda D}{d},{\beta }_2=\frac{\lambda (D+0.20)}{d}$
$\Rightarrow D=0.8m$
$\beta =\frac{\lambda D}{d}$ ; $\lambda =600nm$