Define the term electric field strength.
Two very small metal spheres X and Y are joined by an insulating rod of length $72\,\text{mm}$. A side view of the setup is shown in Fig. 4.1. Sphere X carries a charge of $+3e$ and sphere Y carries a charge of $-3e$, where $e$ is the elementary charge. The rod is supported at its mid-point Z and makes an angle $\theta$ to the horizontal. The rod and spheres have negligible mass and are placed in a uniform electric field. The electric field strength is $5.0 \times 10^{4}\,\text{V m}^{-1}$. This field is directed vertically upwards.
A potential difference of $4.0\,\text{kV}$ is applied between two charged parallel metal plates to produce the electric field. Calculate the separation between the plates.
A potential difference of $4.0\,\text{kV}$ is applied between two charged parallel metal plates to produce the electric field. Calculate the separation between the plates.
Describe how the two plates are arranged. Your answer should also state the sign of the charge on each plate. You may use Fig. 4.1 to help you.
Determine both the magnitude of the force on sphere Y and its direction.
The electric forces on the two spheres create a couple. This couple produces a torque of $6.2 \times 10^{-16}\,\text{N m}$ on the rod. Calculate the angle $\theta$ of the rod to the horizontal.