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 Electronics Paper 1, Nov/Dec 2009
 Questions: 1 2 Main
Weakness/Remedies
Strength

Question 1

The aim of the experiment is to investigate the relationship between the Zener stabilized output voltage as a function of load resistance.

1. Connect the circuit as shown in Figure 2.
2. Ask the Supervisor to check the circuit connection.

Table 2
Vin=12 V constant

 RL(Ω) 100Ω 470Ω 1kΩ 10kΩ Vout(V)
1. Switch on the power supply.
2. Set the input voltage to 12V.Measure and record in Table 2 the output voltage (Vout).
3. Switch off the power supply.
4. Replace the load resistor (RL) with the 470Ω resistor and repeat steps (d) and (e).
5. Repeat steps (f) and (g) for other values of the load resistor (RL) in Table 2.
6. Switch off the power supply.
7. Draw the graph of output voltage (Vout) on the vertical axis against the load resistance (RL) on the horizontal axis.
From the results in Table 2, comment on the effect of changing load resistance (RL) values on the output voltage.
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OBSERVATION

The candidates were expected to connect the circuit as shown above, obtain the voltmeters readings, plot a graph of the output voltage against the load resistance and from the graph explain the effect of changing load resistance values on the output voltage.

 RL(Ω) 100 Ω 470 Ω 1kΩ 10kΩ Vout(V) 5.9 6.3 6.3 6.3
1. With the 10kΩ resistor the output dropped drastically. This is as a result of a high current flowing in the circuit resulting in a higher voltage drop across the 10kΩ resistor. As a result the Zener diode has lost its stabilization effect.

The candidates understood the task, connected the circuit and obtained readings but failed in the theory of diodes and Zener diode characteristics.