A slit of width a is illuminated by white light. For red light `(lambda=6500Å)`, the first minima is obtained at `theta=30^@`. Then the value of a will be

Options

A. (a) `3250Å`
B. (b) `6.5xx10^-4mm`
C. (c) `1.24` microns
D. (d) `2.6xx10^-4cm`

Answer

C

Explanation

For first minima `theta=lambda/a` or `a=lambda/theta`
`:. a=(6500xx10^-8xx6)/(pi)` (As `30^@=pi/6` radian)
`=1.24xx10^-4cm=1.24` microns