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

ε₀ = 8.85 x 10⁻¹² Fm⁻¹

1. Draw a diagram of a uniform electric field between two plates, showing the field lines and the equipotentials.

2. Do the same for the electric field around a point charge.

3. The potential difference between two plates is 100V. What is the potential difference between a point halfway between the plates and one of the plates?

Half of 100 is 50V.

4. What is the electric potential at a point 0.2m from an alpha particle (charge on an electron = -1.6 x 10⁻¹⁹C)?

The charge on an alpha particle is 3.2 x 10⁻¹⁹C.

$V={\frac {Q}{4\pi \epsilon _{0}r}}={\frac {3.2\times 10^{-19}}{4\pi \times 8.85\times 10^{-12}\times 0.2}}=1.44\times 10^{-8}{\mbox{ V}}$

5. What is the electric potential energy of an electron at the negative electrode of an electron gun if the potential difference between the electrodes is 10V?

$U=Vq=10\times -1.6\times 10^{-19}=-1.6\times 10^{-18}{\mbox{ J}}=-10{\mbox{ eV}}$