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In an X-ray tube working at a fixed accelerating potential, the continuous spectrum of X-rays extends over which range of wavelengths?

1. From zero to infinity
2. From a minimum wavelength λ_min to infinity, with λ_min greater than zero
3. From zero up to a finite maximum wavelength λ_max
4. From λ_min to λ_max, where 0 < λ_min < λ_max < ∞

Correct answer: From a minimum wavelength λ_min to infinity, with λ_min greater than zero

Solution

The continuous (bremsstrahlung) spectrum has a sharp short-wavelength cutoff lambda_min = hc/(eV) set by the accelerating potential, and extends from this lambda_min (> 0) up to infinity.

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