1.1. A light-emitting diode (LED) is a diode that emits light when there is a current in it. 

Draw a circuit diagram showing an LED, connected so that it is lit, in series with a battery and a fixed resistor.

1.2. The voltage across the LED when lit is 3.1 V and the current in the LED is 0.030 A.

i) Add to the diagram in (a) to show how these readings were obtained.

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ii) Calculate the value of the resistance of the LED when lit.

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iii) A second identical LED is connected in series with the first LED. The battery and fixed resistor are unchanged.

Describe the effect on

1. the ammeter reading

2. the voltmeter reading across the first LED

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1.3. The diagram shows a power supply with a voltage of 12 V connected in series with a lamp and a heater.

The voltage across the lamp is 3.2 V and the current in the lamp is 1.5 A.

i) Calculate the resistance of the heater.

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ii) Calculate the power of the heater.

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