Each of the resistors in the arrangements below has resistance R. Each arrangement is connected, in turn, to a power supply of constant emf and negligible internal resistance. In which arrangement is the current in the power supply greatest?
Answer/Explanation
Markscheme
C
Examiners report
This was a simple question yet a good number of candidates opted for A, showing perhaps that they had not read the question carefully (and were answering the question: In which arrangement is the resistance greatest?)
Two resistors of resistance 10 Ω and 20 Ω are connected in parallel to a cell of negligible internal resistance.
The energy dissipated in the 10 Ω resistor in one second is Q. What is the energy dissipated in one second in the 20 Ω resistor?
A. \(\frac{Q}{4}\)
B. \(\frac{Q}{2}\)
C. 2Q
D. 4Q
Answer/Explanation
Markscheme
B
Examiners report
Power is inversely proportional to R when the potential difference is constant (as here) and proportional to R if the current is held constant. Many candidates were confused by this.
A battery of emf 12 V and negligible internal resistance is connected to a resistor of constant resistance 6 Ω, an ideal ammeter and an ideal voltmeter.
What is the reading on the ammeter and on the voltmeter?
Answer/Explanation
Markscheme
D
Three parallel wires, X, Y and Z, carry equal currents. The currents in X and Z are directed into the page. The current in Y is directed out of the page.
Which arrow shows the direction of the magnetic force experienced by wire Z?
Answer/Explanation
Markscheme
A
Point P is at the same distance from two charges of equal magnitude and opposite sign.
What is the direction of the electric field at point P?
Answer/Explanation
Markscheme
A
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