Electronics Paper 2, Nov/Dec. 2013

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Questions:	1	2	Main

General Comments
Weakness/Remedies
Strength

Question 2

Question 2

Connect the circuit as shown in figure 2.
Ask the supervisor to check the circuit connection.

Copy Table 2 into your answer booklet.

Table 2

R (k?)	IB(mA)	IC(mA)
220
330
470
560
820

Connect the resistor R1 to the 220 k? resistor.
Switch on the power supply unit.
Read and record in Table 2, the current IB and its corresponding IC.
Repeat steps (d) to (f) for the other values of resistance in Table 2.
Switch off the power supply unit.
Plot a graph of IC (mA) on the vertical axis against IB (mA) on the horizontal

axis.

Determine the slope of the graph.
Comment briefly on the slopes of the graphs drawn in experiment 1 and

experiment 2.

_____________________________________________________________________________________________________

OBSERVATION

The candidates were expected to connect the circuit as shown, measure and record the values of IB and IC, plot a graph of IC (mA) against IB(mA), determine and comment on the slope.
The expected answers were:
(f)

R (k?)	IC(mA)	IB(µA)
220	7.26	23.00
330	4.88	15.00
470	3.42	11.00
560	2.85	8.00
820	1.92	6.22

Note: Range of values                IB min. = 6.4 µA, IB max    = 23 µA
                   for Exp. 2                        IC min = 0.64 mA, IC max = 6.9 mA
          (j) Slope of graph: Range of values of β is (100 – 350)

(k) Comment on slopes
          Slope
                   β        =
               Both graphs are linear and the slopes are positive. is a linear constant.

As reported by the Chief Examiner, the readings obtained by many of the candidates that answered this question showed that they did not know how to adjust meter settings to correspond to indicated values of measured quantities.