Wave Optics Ques 18
18. In Young’s double slit experiment, the fringe width is found to be $0.4$ $ mm$. If the whole apparatus is immersed in water of refrative index $\frac{4}{3}$, without disturbing the geometrical arrangement, the new fringe width will be
[1990]
(a) $0.30 $ $mm$
(b) $0.40 $ $mm$
(c) $0.53 $ $mm$
(d) $450$ microns
Show Answer
Answer:
Correct Answer: 18.(a)
Solution:
- (a) $\beta^{\prime}=\frac{\beta}{\mu}=\frac{0.4}{\frac{4}{3}}=0.3 $ $mm$
If the whole YDSE set up is taken in another medium then $\lambda$ changes. So $B$ changes.
In water $\lambda \omega=\frac{\lambda_a}{\mu_w}$
$ \Rightarrow \quad \beta \omega=\frac{B_a}{\mu_w}=\frac{3}{4} B_a $
BETA
