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An X-ray tube is operated at 1.24 million volt. The shortest wavelength of the produced photon will be

Asked in JEE Main 24th Feb 2nd Shift 2021 · X-ray cut-off wavelength

(1) 10⁻¹ nm
(2) 10⁻⁴ nm
(3) 10⁻² nm
(4) 10⁻³ nm

Answer: (4) 10⁻³ nm

Step-by-step solution

At the cut-off the electron's whole kinetic energy eV becomes one photon.

λₘᵢₙ=(1240 eV nm)/(1.24×10⁶ eV).

λₘᵢₙ=10⁻³ nm.

Why the other options are wrong

(1) comes from an exponent slip of two places
(2) comes from an exponent slip of one place the other way
(3) comes from an exponent slip of one place

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