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 Electronics Paper 2, Nov/Dec. 2013
 Questions: 1 2 Main
Weakness/Remedies
Strength

Question 1
• Question 1

AIM: The aim of both experiments is to determine d.c. current gain of a Bipolar Junction Transistor(BJT).

1.   Connect the circuit as shown in Figure 1.
2.   Ask the Supervisor to check the circuit connection.
3.   Copy Table 1 into your answer booklet.

Table 1

 R(k?) IB(mA) IC(mA) 220 330 470 560 820
1.   Connect the resistor R1 to the 220 k? resistor.
2.   Switch on the power supply unit.
3.   Read and record in Table 1, the current IB  and its corresponding IC. .
4.   Repeat steps (d) to (f) for the other values of resistance in Table 1.
5.   Switch off the power supply unit.
6.   Plot a graph of IC (mA) on the vertical axis and IB (mA) on the

horizontal  axis.

1.   Determine the slope of the graph.
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OBSERVATION

The candidates were expected to connect the circuit as shown, measure and record the current readings in mA, plot a graph of Ic against IB and determine the slope of the graph.
The expected answers were:
Table 1
(f)

 R (k?) IC(mA) IB(µA) 220 4.60 23.0 330 3.06 15.0 470 2.10 11.0 560 1.74 8.0 820 1.14 6.2

Note:  Range of values                  IB min. = 6.4 µA, IB max    = 23 µA
for Exp. 1                                 IC min  =  0.64 mA, IC max = 9.2 mA

(j) Slope Of Graph:
Range of values of  is (150 – 400)
The Chief Examiner reported that the many candidates showed good knowledge of components’ connection but were inadequate in the given answers.