Question

A slit width a is illuminate by white light. The first minimum for red light (λ = 6500 A°) will fall at O = 30 when a will be

Options

• 3250 A°

• 6 – 5 × 10^–4 mm

• 1.3 micron

• 2.6 × 10^–4 m

Answer 1

1.3 micron

Explanation:

For first minimum

a sin θ = `1 lambda`

`a = x/sin theta = (6.5 xx 10^-7)/sin 30^circ` m

= `13 xx 10^-7` m

= 1.3 micron.