Q. In Young's double slit experiment the separation d between the slits is 2 mm, the wavelength $\lambda$ of the light used is 5896 Å and distance D between the screen and slits is 100 cm. It is found that the angular width of the fringes is 0.20°. To increase the fringe angular width to 0.21° (with same $\lambda$ and D) the separation between the slits needs to be changed to
A) 2.1 mm
B) 1.9 mm
C) 1.8 mm
D) 1.7 mm
Explanation
[Solution] Angular width $= \lambda/d$, so $d_2 = d_1 \times \frac{0.20}{0.21} = 2 \times 0.952 \approx 1.9$ mm. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.