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A slit of width $a$ is illuminated by white light. For red light $(\lambda=6500 A)$, the first minima is obtained at $\theta=30^{\circ}$. Then the value of $a$ will be
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1.24 microns
For first minima ${ }^{\theta=\frac{\lambda}{a}}$ or $\quad a=\frac{\lambda}{\theta}$
$\therefore a=\frac{6500 \times 10^{-8} \times 6}{\pi} \quad\left(\right.$ As $30^{\circ}=\frac{\pi}{6}$ radian $)$
$=1.24 \times 10^{-4} \mathrm{~cm}=1.24$ microns
$\therefore a=\frac{6500 \times 10^{-8} \times 6}{\pi} \quad\left(\right.$ As $30^{\circ}=\frac{\pi}{6}$ radian $)$
$=1.24 \times 10^{-4} \mathrm{~cm}=1.24$ microns
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