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Question: Answered & Verified by Expert
Interference was observed in an interference chamber when air was present. Now, the chamber is evacuated and if the same light is used, a careful observation will show
PhysicsWave OpticsJIPMERJIPMER 2008
Options:
  • A no interference
  • B interference with bright band
  • C interference with dark bands
  • D interference in which breadth of the fringe will be slightly increased
Solution:
1927 Upvotes Verified Answer
The correct answer is: interference in which breadth of the fringe will be slightly increased
When chamber is evacuated, the refractive index ( $\mu$ ) decreases. Therefore, wavelength $\left(\lambda \propto \frac{1}{\mu}\right)$ increases.
Now, fringe width is given by
$\begin{aligned} & \beta=\frac{\lambda D}{d} \\ \Rightarrow \quad & \beta \propto \lambda\end{aligned}$
Therefore, as wavelength increases, the fringe width will increase.

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