A student investigates a circuit containing different combinations of resistors to determine the resistance RRR of resistor XXX.
In Circuit A, resistor XXX is connected in series with a single 5.0 Ω5.0\,\Omega5.0Ω resistor, an ammeter, and a power supply. A voltmeter is connected in parallel with resistor XXX.
For Circuit B, a second 5.0 Ω5.0\,\Omega5.0Ω resistor is connected in series with the first resistor between terminals P and Q.
For Circuit C, a third 5.0 Ω5.0\,\Omega5.0Ω resistor is connected in series with the other two resistors between terminals P and Q.
The student obtains the following results:
| Circuit | Potential difference VVV / V\text{V}V | Current III / A\text{A}A |
|---|---|---|
| A | 3.83.83.8 | 0.370.370.37 |
| B | 2.92.92.9 | 0.280.280.28 |
| C | 2.32.32.3 | 0.220.220.22 |
Calculate the value of the resistance RRR of resistor XXX for each circuit (A, B, and C) using the equation:
R=VI R = \frac{V}{I} R=IVGive your answers to 3 significant figures.
A student suggests that the value of RRR should be constant. State whether your results from part (a) support this suggestion. Justify your statement by comparing the calculated values of RRR (assume a limit of experimental accuracy of 10%10\%10%).
The student wants to check the results by using one other possible arrangement of the three 5.0 Ω5.0\,\Omega5.0Ω resistors between terminals P and Q.
The student decides to replace the resistor combinations between P and Q with a single variable resistor to vary the current in the circuit.
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.