Question 1

AIM: Verification of Ohm’s law in a d.c. circuit.

(a) Connect the circuit as shown in Figure 1.

(b) Ask your supervisor to check the circuit connection.

(c) Copy Table 1 into your answer booklet. ;

Table 1

         

Number of cells	V(V)	I (mA)	L(condition of bulbs)
2
3
4
5
6

(d) Close switch S.
(e) Read and record the readings on the ammeter, A and voltmeter, V in Table 1.
(f) State the condition of the bulbs in column L in Table 1.
(g) Open switch S.
(h) Increase the number of cells as shown in Table 1.
(i) Repeat steps (d) to (g) for each cell increment as shown in Table 1.
(j) Plot a graph of voltage V(V) on the vertical axis against current I(mA) on the horizontal axis.
(k) Determine the slope of the graph.
(l) Evaluate the resistance of bulb L1.

 

 

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

         

Number of cells	V(V)	I (mA)	L(condition of bulbs)
2	3.0	80.00	OFF
3	4.5	120.00	DIM/DULL
4	5.9	160.00	BRIGHT
5	7.4	200.00	BRIGHTER
6	8.7	240.00	BRIGHTEST

(k)The slope of the graph was 36.6 ?.
(l) The resistance of the bulb was 12.2 ?.

 The candidates, as reported, were able to obtain the readings and plot the graph. However, many of them got the voltage readings in this question wrong.