Define electric field strength.

1. (a)Define electric field strength.[1]
2. (b)Two very small metal spheres X and Y are connected by an insulating rod of length 72mm. A side view of this arrangement is shown in Fig. 4.1. Sphere X has a charge of +3e and sphere Y has a charge of -3e, where e is the elementary charge. The rod is held at its mid point Z at an angle θ to the horizontal. The rod and spheres have negligible mass and are in a uniform electric field. The electric field strength is 5.0 × 10⁴ V m⁻¹. The direction of this field is vertically upwards.
3. (b)(i).1The electric field is produced by applying a potential difference of 4.0kV between two charged parallel metal plates. Calculate the separation between the plates.[2]
4. (b)(i).2Describe the arrangement of the two plates. Include in your answer a statement of the sign of the charge on each plate. You may draw on Fig. 4.1.[2]
5. (b)(ii)Determine the magnitude and direction of the force on sphere Y.[2]
6. (b)(iii)The electric forces acting on the two spheres form a couple. This couple acts on the rod with a torque of 6.2 × 10⁻¹⁶ Nm. Calculate the angle θ of the rod to the horizontal.[2]

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