Q124 / 200 · JIPMER 2008 · Physics

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

  • A
    no interference
  • B
    interference with bright band
  • C
    interference with dark bands
  • Correct answer
    D
    interference in which breadth of the fringe will be slightly increased

Solution

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.

Hence, the correct answer is option: 'D'.

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