waecE-LEARNING
Electronics Paper 1, May/June 2012  
Questions: 1 2   Main
General Comments
Weakness/Remedies
Strength



















Question 1

AIM: To determine the equivalent resistance of a circuit.


                                         Figure 1

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

Table 1

Voltmeter reading (V)

Ammeter reading (mA)

3.0

 

4.0

 

6.0

 

8.0

 

9.0

 

12.0

 

  1.   Close switch S1.
  2.   Adjust the power supply to obtain a reading of 3 V.
  3.   Read and record the readings of the ammeter and voltmeter as in Table 1.
  4.   Repeat steps (e) and (f) for the other voltage values in Table 1.
  5.   Plot a graph of voltage (V) on the y-axis against current (I) on the x-axis.
  6.   Determine the slope (L1) of the graph.
  7.   State the equivalent resistance of the circuit.

 

_____________________________________________________________________________________________________
OBSERVATION

Comment briefly on the:

(i)      voltage and current readings;

(ii)      input and output voltages

The candidates were expected to connect the circuit as shown, measure and record the current (mA) and voltage (V) in Table 1 and comment briefly on both readings and the input and output voltages.
The expected answers were:
(c)                                            Table 1


Resistance RB (Ω)

 

1 kΩ

 

2 kΩ

 

4 kΩ

 

6 kΩ

 

8 kΩ

 

10 kΩ

Current (mA)

6.273

3.532

2.058

1.599

1.366

1.188

Voltage (V)

4.973

4.961

4.928

4.119

1.780

0.000

(i) i.  current decreased with increase in resistance; voltage changed with current up to I = about 2 mA and remained fairly steady thereafter. That appears to define the Zener output.
ii.  input voltage was set at 12 V(DC) and output voltage varied as described above.

Only a few candidates recorded measurement results of the type required. Majority of the candidates could not comment accurately on the voltage and current readings and the input and output readings
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