Paper 2 Electric Fields Drills

Q1 Coulomb Force and Field

Two small charged spheres carry charges $+3.0\mathrm{nC}$ and $-8.0\mathrm{nC}$. Their centres are separated by $0.120\mathrm{m}$ in air. Take $1/(4\pi {ϵ}_0)=8.99\times 10^9\mathrm{N}{\mathrm{m}}^2{\mathrm{C}}^{-2}$.

1. Calculate the magnitude of the force between the spheres. [3]
2. State whether the force is attractive or repulsive. [1]
3. Calculate the electric field strength at the position of the $-8.0\mathrm{nC}$ charge due to the $+3.0\mathrm{nC}$ charge. [2]

Q2 Uniform Field Between Plates

Parallel plates have p.d. $1.50\mathrm{kV}$ and separation $6.0\mathrm{mm}$.

1. Calculate the uniform electric field strength between the plates. [2]
2. Find the force on an electron between the plates. Take $e=1.60\times 10^{-19}\mathrm{C}$. [2]
3. State the direction of force on the electron relative to the electric field. [1]

Q3 Potential and Energy

A charge $q=+2.0\mu \mathrm{C}$ moves from point A at potential $+120\mathrm{V}$ to point B at potential $+35\mathrm{V}$.

1. Calculate the change in electric potential energy. [3]
2. State whether the electric field does work on the charge during this motion. [2]
3. Explain why electric potential is treated as a scalar. [1]