Question

A quantum of electromagnetic radiation has an energy of 2.0 kev. what is its frequency? planck's constant is 6.63 × 10−34 j · s. answer in units of hz.

Answer 1

A quantum of electromagnetic radiation is called photon, and the energy of a photon is given by
$E=hf$ (1)
where h is the Planck constant and f is the frequency of the photon.

In this problem, the photon energy is
$E=2.0 keV=2.0 \cdot 10^3 eV=3.2 \cdot 10^{-16} J$
If we re-arrange equation (1), we can find the energy of the photon:
$f= \frac{E}{h}= \frac{3.2 \cdot 10^{-16} J}{6.6 \cdot 10^{-34} Js}=4.8\cdot 10^{17} Hz$