Question 1

AIM: Investigation of the relationship between frequency and current in series LC  circuit.

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

Table 1

Frequency, f (Hz)	300	600	900	1200	1500	1800	2100	2400	2700	3000
Current, I (mA)

1. Adjust the frequency of the generator to 300 Hz as shown in Table 1.
2. Read and record the ammeter 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 current I (mA) on the vertical axis against frequency f (Hz)

on the  horizontal axis.

1.  Determine from the graph the resonant frequency.
2. Comment on the current at resonance.

The candidates were expected to connect the circuit as shown in Fig.1, measure and record in Table 1 current readings, plot the graph f(Hz) versus I(mA), determine the resonant frequency and the associated current from the graph.

The expected answers were:
Table 1

Frequency, f (Hz)	300	600	900	1200	1500	1800	2100	2400	2700	3000
Current, I (mA)	0.009	0.020	0.030	0.040	0.080	0.440	0.200	0.080	0.050	0.030

The candidates, as reported, understood the question and carried out the actions required. But unfortunately, some of the candidates did not record accurate readings, so their graph and deductions were wrong.