Question
Find the angular separation between the consecutive bright fringes in a Young's double slit experiment with blue-green light of wavelength 500nm. The separation between the slits is $2.0 × 10^{-3}$m.

Answer

Given that, $\lambda=500\text{nm}=500\times10^{-9}\text{m}$ and $d = 2 × 10^{-3}m$

As shown in the figure, angular separation $\theta=\frac{\beta}{\text{D}}=\frac{\lambda\text{D}}{\text{dD}}=\frac{\lambda}{\text{d}}$
So, $\theta=\frac{\beta}{\text{D}}=\frac{\lambda}{\text{d}}=\frac{500\times10^{-9}}{2\times10^{-3}}=250\times10^{-6}$
$= 25 × 10^{-5}$ radian $= 0.014$ degree.

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