A-LevelPhysicsD.C. circuits9702/12 · Feb/Mar 2019 · Q361 Mark
A cell of internal resistance r and electromotive force (e.m.f.) E is connected in series with a resistor of resistance R. [Figure 36.1] The resistance R and the e.m.f. E remain fixed. The internal resistance r of the cell changes over time. Which graph best shows the variation of the current I in the circuit with the internal resistance r?
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
A[Graph A: I vs r, current decreases as r increases, with the curve flattening out (concave up).]
B[Graph B: I vs r, current decreases as r increases, with the curve getting steeper (concave down).]
C[Graph C: I vs r, current decreases linearly as r increases.]
D[Graph D: I vs r, current is constant for a while, then decreases as r increases.]
✓ Correct answer
B: [Graph B: I vs r, current decreases as r increases, with the curve getting steeper (concave down).]
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