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An electron of mass m and charge e starts from rest and is accelerated by a uniform electric field E. If relativistic effects are neglected, the time rate of change of its de Broglie wavelength at time t is

1. -h/(eEt²)
2. -eht/E
3. -mh/(eEt²)
4. -h/(eE)

Correct answer: -h/(eEt²)

Solution

v = (eE/m)t so p = eEt and lambda = h/p = h/(eEt). Then d(lambda)/dt = -h/(eEt^2).

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