A student investigates the resistance of a diode when different currents flow through it. The student sets up the circuit shown in Fig. 1.1. power source + A P X Y Fig. 1.1

1. (a)The student connects a voltmeter into the circuit to measure the potential difference (p.d.) across the diode. On Fig. 1.1, draw the symbol for a voltmeter connected to measure the p.d. across the diode.[1]
2. (b)The student: • uses a connecting lead to connect the terminals X and Y together • closes the switch • records the voltmeter reading V • records the ammeter reading I • opens the switch and removes the connecting lead. Fig. 1.2 shows the readings on the voltmeter and the ammeter. 1 2 0 V A 1 Fig. 1.2 Record the readings shown in Fig. 1.2 in the top row of Table 1.1.[2]
3. (c)Calculate the resistance R of the diode using the equation: R = V / I Record your answer in the top row of Table 1.1 to an appropriate number of significant figures.[2]
4. (d)The student: • connects a 3.3Ω resistor between terminals X and Y • closes the switch • records the voltmeter reading V in Table 1.1 • records the ammeter reading I in Table 1.1 • opens the switch and removes the 3.3Ω resistor • repeats this procedure for resistors of 6.8Ω and 10Ω. Complete Table 1.1 by inserting the missing values.[2]
5. (e)(i)As the resistance between terminals X and Y is changed, the current in the circuit changes. Examine the results shown 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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