Stage lamp Dimmer control (variable resistor) Circuit diagram 12 V + Variable resistor Lamp A 0.50 A The diagram shows a theatre technician using a dimmer c...

The diagram shows a theatre technician using a dimmer control for a stage lamp. The dimmer contains a variable resistor. Turning the control changes the resistance in series with the lamp, so the current and the brightness can be adjusted during a performance. At the start of a scene, the lamp has a potential difference of 12 V and a current of 0.50 A. The technician needs a lower light level without changing the battery pack. Fig. 1 shows the lamp, variable resistor, ammeter and battery. The lamp transfers electrical energy mainly to light and thermal energy.

(a) What is the resistance of the lamp at this setting? [2]
(b) Which way does the lamp brightness change when the current decreases? [1]
(c) Sketch a circuit symbol for a variable resistor. [1]

A maintenance worker examines the plug of an electric hedge trimmer shown in Fig. 1. The trimmer is used outdoors and has a metal cutting blade but a double-insulated plastic body. Its cable has live, neutral and earth wires. A fuse is fitted in the plug on the live wire. If the cable is cut accidentally, a fault current could transfer a large amount of electrical energy to heating. The worker checks that the wire grips hold the outer insulation and that no copper wire is exposed. The diagram shows the inside of the plug and the cable connections.

(a) Which wire is normally coloured brown? [1]
(b) What is the purpose of a fuse in the plug? [2]
(c) When should the trimmer be disconnected from the mains during maintenance? [1]