A slit of width a is illuminated by white light. The first minimum for red light (λ = 6500 Å) will fall at θ = 30° when a will be
Answer & explanation
Correct answer: option 3
Condition for 1st minimum is
a Sin$\theta = \lambda$
a $\times \frac{1}{2} = 6500 A^o$
a = 13000 $A^o$ = 1.3 micron