Two flat, parallel equipotential surfaces, at $10\ \text{V}$ and $20\ \text{V}$, are $5\ \text{cm}$ apart in a uniform electric field, as shown in the figure. The electric field, and the work needed to move a $2\ \mu\text{C}$ charge $3\ \text{cm}$ along the $20\ \text{V}$ surface, are

Fig. 1: Two parallel equipotential surfaces seen edge on, 10 V on the left and 20 V on the right, 5 cm apart. A 2 microcoulomb charge on the 20 V surface is moved 3 cm along it.