Q1 A student investigated the variation of the current I flowing through a semiconductor diode for a range of different values of potential difference V, with the diode initially positioned in forward bias.
Table 19.4 V / V I / mA
0.2 1
0.4 3
0.5 0.6 0.7 7
16 (i) Draw a circuit diagram used by the student. (ii) Draw a graph to show how the current varies with the potential difference. (iii) Explain why there is a sharp increase in the slope of the graph as the voltage exceeds 0.6 V.
(iv) In order to plot a graph of current against voltage for a diode in reverse bias, the student made a number of changes to the circuit. Draw the new circuit diagram and sketch a typical graph for the reverse bias diode.
Q2 A student measured the resistance R of the thermistor at different temperatures . The table shows the measurements recorded by the student. Table 19.5
/ C R /
10 20 30 250 120 60
45 25
60 15
75 11
(i) Explain, with the aid of a labelled diagram, how the student collected the data.
(ii) Draw a graph on graph paper of resistance R against temperature . Put temperature on the horizontal axis.
(iii) Using your graph, estimate the temperature of the thermistor when the resistance was 50 .
(iv) State two precautions that were taken to ensure that the temperature that was taken was the same as the temperature of the thermistor.
90 9
(15)
(12) (7)
(6) 45 0.8 0.9 90 180
(12) (9) (6)
(13)
‘SECTION B’ SHORT QUESTION
Typical of Question 5 in Leaving Cert. Exam
Q3 Answer all of the following parts (a), (b), (c), etc. (a) What is the difference between intrinsic and extrinsic conduction in semiconductors? (b) What is the difference in response to temperature change in metals and semiconductors? (c) Give two uses for a thermistor.
