An X-ray photon has a wavelength of 0.10 nm. What is its energy in keV (h = 6.63 × 10⁻³⁴ J s, c = 3.0 × 10⁸ m/s, e = 1.6 × 10⁻¹⁹ C)?
Correct answer C. 12.4 keV
Explanation
E = hc/λ = 1.989 × 10⁻²⁵/1.0 × 10⁻¹⁰ = 1.99 × 10⁻¹⁵ J. Dividing by 1.6 × 10⁻¹⁹ gives 1.24 × 10⁴ eV = 12.4 keV.
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