Answer to Question #138236 in Electric Circuits for Karen

Question

Find the electric potential difference Ve required to stop an electron (called a “stopping potential”) moving with an initial speed of 2.85 x 107 m/s. Would a proton travelling at the same speed require a greater or lesser magnitude of electric potential difference? Explain.

Answer 1

Since the energy $W=U\times q$ , where $U$ is the potential difference, and $q$ is the charge, and the kinetic energy $E=\frac{m\times v^2}{2}$ , then $U\times q=\frac{m\times v^2}{2}$ , hence $U=\frac{m\times v^2}{2\times q}=\frac{9.1\times 10^{-31}\times (2.85\times10^7)^2}{2\times 1.6\times 10^{-19}}\approx2309.84$ V.

A proton will require a larger potential difference because it has a larger mass than an electron.