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To increase the de Broglie wavelength of an electron from 0.5×10⁻¹⁰ m to 1×10⁻¹⁰ m, its energy should be ______.

Asked in GUJCET 2016; GUJCET 2019 · Same or changed energy

Answer: (4) decreased to one-fourth

Step-by-step solution

Given: λ₁ = 0.5×10⁻¹⁰ m and λ₂ = 1×10⁻¹⁰ m, so λ₂ = 2λ₁.

Idea: λ = h/p = h/(√2mK), so K = (h²)/(2mλ²) ∝ 1/(λ²).

(K₂)/(K₁) = ((λ₁)/(λ₂))² = (1/2)² = 1/4

So the energy must be decreased to one-fourth of its value.

Why the other options are wrong

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