A-level Physics (Advancing Physics)/Electric Potential Energy/Worked Solutions

k = 8.99 x 10⁹ Nm²C⁻²

1. Convert 5 x 10⁻¹³ J to MeV.

$\frac{5\times 10^{-13}}{1.6\times 10^{-19}}=3125000\text{ eV}=3.125\text{ MeV}$

2. Convert 0.9 GeV to J.

$0.9\times 10^9\times 1.6\times 10^{-19}=1.44\times 10^{-10}\text{ J}$

3. What is the potential energy of an electron at the negatively charged plate of a uniform electric field when the potential difference between the two plates is 100V?

${ϵ}_{elec}=V_{elec}q=100\times 1.6\times 10^{-19}=1.6\times 10^{-17}\text{ J}=0.1\text{ keV}$

4. What is the potential energy of a 2C charge 2 cm from a 0.5C charge?

${ϵ}_{elec}=\frac{kQq}{r}=\frac{8.99\times 10^9\times 2\times 0.5}{0.02}=4.5\times 10^{11}\text{ J}$

Remember, coulombs are big!

5. What is represented by the gradient of a graph of electric potential energy against distance from some charge?

Force exerted on the charge with that energy.