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

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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.

Field lines equipotentials parallel plates.svg

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

Electric field point lines equipotentials.svg

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_0r} = \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}