Verified Solution • 2025–26 Session moderate

QJEEM20Ph8172: JEE Main 2020 Physics - Class 12 JEEM20Ph8172 Solution: An electron of mass m and magnitude of charge

An electron of mass m and magnitude of charge |e| initially at rest gets accelerated by a constant electric field E. The rate of change of de-Broglie wavelength of this electron at time t ignoring relativistic effects is :

Multiple Choice Options

  • A −h∣e∣Et{{ - h} \over {\left| e \right|Et}}
  • B −h∣e∣Et{{ - h} \over {\left| e \right|E\sqrt t }}
  • C −h∣e∣Et2{{ - h} \over {\left| e \right|E{t^2}}}
  • D ∣e∣Eth{{\left| e \right|Et} \over h}

Step-by-Step Verified Solution

F = |e| E

a=Fma = {F \over m} = ∣e∣Em{{\left| e \right|E} \over m}

V = at=at = ∣e∣Emt{{\left| e \right|E} \over m}t

λ\lambda = hmV{h \over {mV}} = h∣e∣Et{h \over {\left| e \right|Et}}

dλdt{{d\lambda } \over {dt}} = −h∣e∣Et2{{ - h} \over {\left| e \right|E{t^2}}}

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