CIE iGCSE Co-Ordinated Science P4.3.2 Series and parallel circuits Exam Style Questions Paper 1
▶️ Answer/Explanation
The diagram shows the two resistors connected in parallel. For resistors in parallel, the combined resistance is calculated using the formula \(\frac{1}{R_{\text{total}}} = \frac{1}{R_1} + \frac{1}{R_2}\). Substituting the values gives \(\frac{1}{R_{\text{total}}} = \frac{1}{3.0} + \frac{1}{6.0} = \frac{2}{6} + \frac{1}{6} = \frac{3}{6} = \frac{1}{2}\), so \(R_{\text{total}} = 2.0\,\Omega\). This is less than either individual resistor, which is a key characteristic of parallel circuits. Option A is the correct answer. Options B and C represent incorrect parallel calculations, and option D would be the combined resistance if the resistors were connected in series.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
Increasing the number of cells increases the voltage (potential difference) across the motor, which increases the current flowing through it. Decreasing the resistance of the variable resistor also allows more current to flow. Since the speed of a motor increases with more current, both actions together will increase the motor’s speed. Therefore, option C is correct.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
In a parallel circuit, the combined resistance is always less than the smallest individual resistance because there are multiple paths for current to flow.
Therefore, the combined resistance must be less than 12 Ω. It cannot be equal to the sum (series) or between the values.
✅ Answer: (D)
Therefore, the combined resistance must be less than 12 Ω. It cannot be equal to the sum (series) or between the values.
✅ Answer: (D)
▶️ Answer/Explanation
When resistors are connected in parallel, the combined resistance is always less than the resistance of the smallest individual resistor. This is because the current has multiple pathways, reducing the overall opposition to current flow. For a \(4.0 \, \Omega\) and \(8.0 \, \Omega\) resistor in parallel, the combined resistance will be less than \(4.0 \, \Omega\).
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
In a parallel arrangement, the branch with the smaller resistance R carries the larger share of the current, so its ammeter reads the higher value.
The combined resistance of resistors R and 2R in parallel is found from \(\dfrac{1}{R_{total}} = \dfrac{1}{R} + \dfrac{1}{2R}\), giving \(R_{total} = \dfrac{2R}{3}\).
This combined resistance is always smaller than the smallest individual resistor, R.
✅ Answer: (C)
The combined resistance of resistors R and 2R in parallel is found from \(\dfrac{1}{R_{total}} = \dfrac{1}{R} + \dfrac{1}{2R}\), giving \(R_{total} = \dfrac{2R}{3}\).
This combined resistance is always smaller than the smallest individual resistor, R.
✅ Answer: (C)