Question

At what angles for the first order diffraction, spacing between two planes respectively are land $\frac{\lambda}{2}$ ?

• A. 0⁰, 90⁰
• B. 90⁰, 0⁰
• C. 30⁰, 90⁰
• D. 90⁰, 30⁰

Answer 1

Answer: (C)

30⁰, 90⁰

Answer 2

n × l = 2d sinq

In first case, 1 × l = 2l sinq

or sinq = $\frac{1}{2}$ = sin 30⁰

or q = 30⁰

In second case, 1 × l = 2 × $\frac{\lambda}{2}$× sinq

or sinq = 1 = sin 90⁰

or q = 90⁰