Question

If you wish to produce 45.0 nm x-rays in the laboratory, what is the minimum voltage you must use in accelerating the electrons?

Answer 1

Law of conservation of energy is what can help us to solve the problem:

$$qV=\frac{hc}{\lambda},\\\space\\ V=\frac{hc}{q\lambda}=\frac{(6.6\cdot10^{-34})(3\cdot10^8)}{(1.6\cdot10^{-19})(450\cdot10^{-9})}=2.8\text{ V}.$$