# Physics MCQ

Question:

An electron initially at rest is accelerated through a potential difference. It is then brought to rest in a collision, and all of its kinetic energy is converted into a single photon of electromagnetic radiation. Which one of the following quantities is not required to find a value for the wavelength of the photon?

A The mass of the electron
B The charge on the electron
C The velocity of electromagnetic waves
D The value of the potential difference

To show this, suppose we accelerate an object of charge $q$ and mass $m$ across a P.D $V$. The energy gained is $q\times V$. As you can see, nowhere is the mass used in the equation. Furthermore $\lambda = \frac{E}{hc}$, and as energy is not dependent on mass, neither is the wavelength.
To show this, suppose we accelerate an object of charge $q$ and mass $m$ across a P.D $V$. The energy gained is $q\times V$. As you can see, nowhere is the mass used in the equation. Furthermore $\lambda = \frac{E}{hc}$, and as energy is not dependent on mass, neither is the wavelength.