Wave Optics - Result Question 21

21. The Young’s double slit experiment is performed with blue and with green light of wavelengths $4360 \AA$ and $5460 \AA$ respectively. If $x$ is the distance of 4th maxima from the central one, then [1990]

(a) $x$ (blue) $=x$ (green)

(b) $x$ (blue) $>x$ (green)

(c) $x$ (blue) $<x$ (green)

(d) $\frac{x \text{ (blue) }}{x \text{ (green })}=\frac{5460}{4360}$

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Answer:

Correct Answer: 21. (c)

Solution:

  1. (c) Distance of nth maxima, $x=n \lambda \frac{D}{d} \propto \lambda$

As $\lambda_b<\lambda_g \quad \therefore \quad x _{\text{blue }}<x _{\text{green }}$

Fringes with red light are thicker than those for blue light.

$\therefore \lambda _{\text{red }}>\lambda _{\text{blue }}$