An investigation is carried out on circuits containing different combinations of two identical resistors, R1R_1R1 and R2R_2R2.
The table below shows the measurements of potential difference VVV across terminals P and Q, and the current III in each circuit:
| Circuit | V / VV\text{ / V}V / V | I / AI\text{ / A}I / A | R / ΩR\text{ / }\OmegaR / Ω |
|---|---|---|---|
| Circuit A | 1.21.21.2 | 0.800.800.80 | |
| Circuit B | 1.81.81.8 | 0.620.620.62 | |
| Circuit C | 2.42.42.4 | 0.410.410.41 |
Calculate the resistance RRR for each circuit using the equation:
R=VI R = \frac{V}{I} R=IVGive your answers to a consistent 2 or 3 significant figures.
Estimate the resistance of a single resistor by calculating RAR_{\text{A}}RA, RBR_{\text{B}}RB, and RCR_{\text{C}}RC[edit] using the expressions:
State whether your results support the suggestion that RAR_{\text{A}}RA, RBR_{\text{B}}RB, and RCR_{\text{C}}RC should be equal. Justify your statement by referring to your values.
The circuits are powered by a supply voltage. A fixed protective resistor, RP=3.0 ΩR_{\text{P}} = 3.0\ \OmegaRP=3.0 Ω, is placed in series with the combination of resistors between P and Q. Explain why this resistor is necessary to protect the circuit, referring to what would happen to the current if RPR_{\text{P}}RP[edit] were removed when testing Circuit A.
Describe the circuit symbol for a variable resistor (rheostat).
State one advantage of using a variable resistor in this experiment rather than regularly changing the supply voltage to obtain multiple readings.
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.