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A particle A of mass m and initial velocity v collides with a particle B of mass 2 m which is at rest. The collision is head on, and elastic. The ratio of the de-Broglie wavelengths λ A to λ B after the collision is -

1. 3 1 B A = λ λ
2. B A λ λ = 2
3. 3 2 B A = λ λ
4. 2 1 B A = λ λ

Correct answer: B A λ λ = 2

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