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

Question 2

AIM: To investigate the voltage gain characteristics of a common emitter amplifier.

(a) Connect the circuit as shown in Figure 2.
(b) Ask the Supervisor to check the circuit connection.
(c) Copy Table 2 into your answer booklet.
                        Table 2

Vin(mv)

Vout(V)

Voltage gain = Vout

 

 

Vin

1.0

 

 

1.5

 

 

2.0

 

 

2.5

 

 

3.0

 

 

3.5

 

 

4.0

 

 


(d) Set the signal generator to 10 kHz sine wave and adjust the input to
obtain a reading of 1 mV.
(e) Measure and record in Table 2 the corresponding value of Vout
(f) Repeat steps (d) and (e) for other values of v; in Table 2.
(g) Complete Table 2 by calculating the voltage gain (Av) for each set of readings.
(h) From your results in Table 2, state whether the frequency of 10 kHz is in
the amplifier's low frequency, mid-frequency, or high frequency.
The candidates were expected to connect the circuit as shown above, obtain the input voltage, output voltage and gain readings and state where the 10 kHz frequency belong.

_____________________________________________________________________________________________________
OBSERVATION

The expected answers were:
      (d)                         Table 2

Vin(mv)

Vout(V)

Voltage gain = Vout

 

 

Vin

1.0

0.198

0.198

1.5

0.297

0.198

2.0

0.396

0.198

2.5

0.494

0.197

3.0

0.593

0.197

3.5

0.691

0.197

4.0

0.789

0.197

(h)Mid- frequency region
As reported by the Chief Examiner, the readings by the very few candidates that answered this question suggested that many candidates do not know how to adjust meter settings to correspond to indicate values of measured quantities.
Very many candidates did not correctly interpret mV as implying 10-³ V, and in same vein could not know the ratio of two voltage quantities as a dimensionless quantity with some surprisingly giving the units as ohms.

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