Applied Electricity 1 , May/June 2012
 Questions: 1 2 Main
Weakness/Remedies
Strength

Question 2

AIM: Investigation of the relationship between frequency and voltage across a                 series LC circuit.

1.   Connect the circuit as shown in Fig. 2.
2.   Set the frequency of the generator to zero (0.0Hz).
3.   Ask the supervisor to check the circuit connection.
4.   Copy Table 2 into your answer booklet.

Table 2

 Frequency, f (Hz) 300 600 900 1200 1500 1800 2100 2400 2700 3000 Voltage, V (V)
1.   Adjust the frequency of the generator to 300 Hz as shown in Table 2.
2.   Read and record the voltmeter reading.
3.   Increase the frequency of the generator by 300 Hz.
4.   Repeat steps (f) and (g) until the frequency is up to 3000 Hz.
5.   Plot a graph of voltage V(V) on the vertical axis against frequency f(Hz) on     the horizontal axis.
6.   Determine from the graph the frequency at which the voltage is minimum.
7.   Comment on the voltage at resonance.

Observation

The candidates were expected to connect the circuit as shown in Figure 2, measure and record in Table 2 the expected readings. They were also required to plot the graph V(V) versus f(Hz), determine the frequency at which the voltage is minimum and comment on the voltage at resonance.

The expected answers were:
Table 2

 Frequency, f (Hz) 300 600 900 1200 1500 1800 2100 2400 2700 3000 Voltage, V (V) 17 8 3 1.6 1 0.7 0.6 0.4 0.3 0.2
The candidates, understood the question and carried out the actions required. Many of the candidates did not get accurate readings, so their graph and deductions were wrong.