Question

LED emitting at wavelength of $2\mu m$ with spectral width of $40\mu m$, used as a coherent source in MIchelson's interferometer to get sustained interference. The maximum optical path difference between two arms of interferometer is($\mu m$)

• A. $50$
• B. $100$
• C. $5$
• D. $10$

Answer 1

The correct option is B $100$

spectral width $({\lambda }_1-{\lambda }_2)=\Delta \lambda =\frac{({\lambda }_{av}{)}^2}{2x}$
So, $x=\frac{(2\times {10}^{-6}{)}^2}{2\times 40\times {10}^{-9}}$
$x=50\mu m$
maximum path difference $2x=100\mu m$