Question

A slit of width a is illuminated by white light. For red light `(λ = 6500 Å)`, the first minima is obtained at θ = 60°. Then the value of a will be ______.

Options

• 3250 Å

• 6.2 x 10^-4 mm

• 0.62 micron

• 2.6 x 10^-4 cm

Answer 1

A slit of width a is illuminated by white light. For red light `(λ = 6500 Å)`, the first minima is obtained at θ = 60°. Then the value of a will be 0.62 micron.

Explanation:

For first minima,

`θ= λ/a or a= λ/θ`

∴ `a=( 6500xx10^-8xx3)/π ...(∵ 60° = π/3 "radian")`

`=0.62xx 10^-4 "cm"`

`=0.62xx 10^-6 m`

=0.62 micron