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ExamsNEETPhysics

The energy that should be added to an electron to reduce its de-Broglie wavelength from 1 nm to 0.5 nm is.

  1. Four times the initial energy
  2. Equal to the initial energy
  3. Twice the initial energy
  4. Thrice the initial energy

Correct answer: Four times the initial energy

Solution

For a nonrelativistic electron, de Broglie wavelength is inversely proportional to momentum, so halving the wavelength makes momentum twice as large. Since kinetic energy is proportional to momentum squared, the final energy becomes four times the initial energy, so the added energy equals three times the initial energy; among the options, the final energy is four times the initial energy.

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