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1.  When a mains lamp is switched on it takes 0.5 seconds for the filament to reach its normal operating temperature. The way in which the current changes during the first second after switching on is shown in the sketch graph below. Mains voltage is 240 V.

 

(a) Calculate the resistance of the filament whilst the lamp is drawing the maximum current.

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(b) Describe how the resistance of the lamp changes after the current has reached its maximum value.

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(c) Calculate the maximum power taken by the lamp.

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(d) Calculate the power of the lamp in normal use.

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(e) Calculate the energy used by the lamp in six hours of normal use.

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2.  The circuit diagram below shows a circuit used to supply electrical energy to the two headlights of a car.

The current through the filament of one car headlight is 3.0A. The potential difference across each of the two headlights is 12 V.

(a) Suggest a suitable fuse for the circuit.

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(b) Calculate the resistance of the headlight filament when in use.

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(c) Calculate the power supplied to the two headlights of the car.

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(d) The fully charged car battery can deliver 72 kJ of energy at 12 V. How long can the battery keep the headlights fully on?

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