Question

The wave number (k), for three em waves (x₁ , x₂ and x₃) has value k₁ , k₂ and k₃ , respectively. It is given that k₁ is less than both k₂ and k₃ while k₂ is greater than k₃ . The three em waves, (x₁ , x₂ , x₃) could then be

(1) infrared rays, uv rays, visible light

(2) visible light, uv rays, γ – rays

(3) radiowaves, visible light, uv rays

(4) microwaves, visible light, γ – rays

Answer 1

(1) infrared rays, uv rays, visible light

We have k = 2π/λ

∴ We must have λ₁ more than both λ₂ and λ₃ .

Also we must have λ₂ less than λ₃ . Hence the three em waves must have their wave lenghts in the order.

λ₁ > λ₃ > λ₂

This ordering of wave lenghts is valid only in option (1). In all the other three options, λ₂ is more than λ₃ .