In this experiment you will investigate the resistance of a diode when different currents flow through it. You are provided with: • a power source • an ammeter • a voltmeter • a diode • a 3.3Ω resistor, a 6.8Ω resistor and a 10 Ω resistor • a switch • a resistor labelled P • two spare connecting leads. The supervisor has set up the circuit shown in Fig. 1.1. [Figure 1.1]

1. (a)• Use a spare connecting lead to connect the terminals X and Y together. • Close the switch. • Record the voltmeter reading V in the top row of Table 1.1. • Record the ammeter reading I in the top row of Table 1.1. • Open the switch and remove the connecting lead.[2]
2. (b)• Use both spare connecting leads to connect the 3.3Ω resistor between terminals X and Y. • Close the switch. • Record the voltmeter reading V in Table 1.1. • Record the ammeter reading I in Table 1.1. • Open the switch and remove the connecting leads and the 3.3Ω resistor.[2]
3. (c)Repeat the procedure in (b) for the resistors of 6.8Ω and 10Ω.[1]
4. (d)Calculate the resistance R of the diode for each pair of readings of V and I, using the equation: R = V/I Record your answers in Table 1.1.[2]
5. (e)(i)As the resistance between terminals X and Y is changed, the current in the circuit changes. Examine your results in Table 1.1. Describe how the change in current affects: the voltage across the diode[1]
6. (e)(ii)the resistance of the diode.[1]
7. (f)A student sets up a circuit using the diagram shown in Fig. 1.1. The student finds that, when the connecting lead is connected across the terminals X and Y and the switch is closed, the ammeter does not give a reading. The ammeter is not broken. Suggest the error that the student has made while assembling the circuit.[1]

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