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When the kinetic energy of an electron is quadrupled, how does the wavelength of its associated de-Broglie wave change?

1. Reduced to a quarter
2. Reduced to half
3. Increased fourfold
4. Doubled

Correct answer: Reduced to half

Solution

The de Broglie wavelength lambda = h/p = h/sqrt(2 m KE) is inversely proportional to sqrt(KE). Quadrupling KE multiplies sqrt(KE) by 2, so lambda is reduced to half, not a quarter.

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