A student investigates the electrical resistance of filament lamps.
The student connects a single lamp L1 L_1\,L1 to a power supply. The potential difference across the lamp is V1=6.0 VV_1 = 6.0\text{ V}V1=6.0 V and the current in the circuit is I1=0.50 AI_1 = 0.50\text{ A}I1=0.50 A. Calculate the resistance R1 R_1\,R1 of the lamp.
The student then connects three identical lamps L1L_1L1, L2L_2L2, and L3 L_3\,L3 in series. The total potential difference across all three lamps is V3=6.0 VV_3 = 6.0\text{ V}V3=6.0 V and the current in the circuit is I3=0.25 AI_3 = 0.25\text{ A}I3=0.25 A. Calculate the combined resistance R3 R_3\,R3 of the three lamps connected in series.
A second student suggests that the combined resistance R3 R_3\,R3 of the three identical lamps in series should be given by the equation R3=3×R1R_3 = 3 \times R_1R3=3×R1. State whether the results from (a) and (b) agree with this suggestion. Justify your answer by comparing the values.
The student now wishes to connect the three lamps in parallel so that their behavior can be compared. Describe how to connect the components in a circuit consisting of a power supply, a switch, an ammeter, three lamps in parallel, a voltmeter to measure the potential difference across the lamps, and a variable resistor to control the total current in all three lamps.
136 exam-style questions on CIE IGCSE Physics 4.3 Electric circuits, covering 4.3.1a Circuit diagrams and circuit components, 4.3.2a Series circuits, 4.3.2b Parallel circuits, 4.3.2c Current and potential difference in circuits, 4.3.2d Combined resistance of resistors in parallel, and 4.3.3 Action and use of circuit components. Each one has a worked solution and a mark scheme showing where the marks go.