(a)[1]
Define electric field strength in terms of force per unit positive charge.
(b)
In a vacuum, two horizontal metal plates are separated by $20\,\text{mm}$. A potential difference of $1.5\,\text{kV}$ is applied across the plates, as shown in Fig. 4.1. A charged oil drop of mass $5.0 \times 10^{-15}\,\text{kg}$ is held stationary by the electric field.
(b(i))[2]
On Fig. 4.1, draw lines that show the electric field between the plates.
(b(ii))[1]
Calculate the electric field strength between the plates.
(b(iii))[4]
Calculate the charge on the drop.
(b(iv))[2]
The potential of the upper plate is increased. Describe and explain how the drop then moves.