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Electronics Paper 1, Nov/Dec 2010  
Questions: 1 2   Main
General Comments
Weakness/Remedies
Strength

Question 1

AIM: To examine d.c. conditions of a common emitter amplifier.

(a) Connect the circuit as shown in Figure 1.                          Figure 1
(b) Ask the Supervisor to check the circuit connection.
(c) Copy Table 1 into your answer booklet.

 

VBE(V)

VEE(V)

VcE(V)

Measured

 

 

 

Calculated

 

 

 


(d) Measure and record in Table 1 the voltages VBE, VEE and VcE.
(e) Using the following expressions:
(i)VBE = VcE / (R1 + R2) x R2
(ii)VcE =VcE - IcR3;
(iii)VEE = VBE- 0.7 V.
Calculate and record in Table 1:
(i)VBE,
(ii)VEE
(Hi)VcE
[Take Ic ˜ IE = VEE / R4

(f) Explain briefly, why the two sets of results in Table 1 are different.

_____________________________________________________________________________________________________
OBSERVATION

The candidates were expected to connect the circuit as shown above, measure and record in Table 1 the voltages VS& VEE and Vcc using step( e) and state the difference between the measured and calculated values.
The expected answers were:

 

VBE(V)

VEE(V)

VcE(V)

Measured

2.307

1.652

6.126

Calculated

2.44

1.74

5.78


(f) The difference in the readings was as a result of the tolerance of the bias resistor OR Meter loading effect/sensitivity
Many candidates obtained useful calculated results, but only a few recorded measurement results of the type required. And almost all the candidates could not accurately account for the differences in measured and calculated values.

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