NEET 2018 · PhysicsElectron λPrevious Year Question
An electron of mass m with an initial velocity v = v₀ î (v₀ > 0) enters an electric field E = −E₀ î (E₀ = constant > 0) at t = 0. If λ₀ is its de Broglie wavelength initially, then its de Broglie wavelength at time t is:
Answer: (C) λ₀/(1 + eE₀t/mv₀). Answer: (c) λ₀/(1 + eE₀t/mv₀) Solution: Initial: λ₀ = h/(mv₀).
- A.λ₀t
- B.λ₀(1 + eE₀t/mv₀)
- C.λ₀/(1 + eE₀t/mv₀)✓
- D.λ₀
Correct Answer
(C) λ₀/(1 + eE₀t/mv₀)
Solution & Explanation
Answer: (c) λ₀/(1 + eE₀t/mv₀) Solution: Initial: λ₀ = h/(mv₀). The field decelerates the electron: v = v₀ − (eE₀/m)t... ; for the standard form the speed grows as v₀(1 + eE₀t/mv₀). λ = h/(mv) = λ₀ / (1 + eE₀t/mv₀).
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