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If the momentum of electron is changed by P, then the de Broglie wavelength associated with it changes by 0.5%. The initial momentum of electron will be:

1. 200 P
2. 400 P
3. P/200
4. 100 P

Correct answer: 400 P

Solution

The de Broglie wavelength is inversely proportional to momentum (λ = h/p). A 0.5% change in wavelength corresponds to a 0.5% change in momentum. Let the initial momentum be P₀. The change in momentum ΔP = 0.005P₀. Given ΔP = P, solving gives P₀ = P/0.005 = 400P.

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