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IBDP Physics- B.5 Current and circuits- IB Style Questions For SL Paper 2 -FA 2025

IBDP Physics SL Paper 2 -FA 2025- All Chapters

Question

The graph illustrates how the current \(I\) varies with the potential difference \(V\) for an ohmic resistor P and a non-ohmic component Q.
(a) Determine the resistance of P.
(b) Describe how the resistance of Q changes as the current through it increases.
P and Q are connected in a circuit with a cell of negligible internal resistance, as shown. The ammeter and voltmeter are ideal. The voltmeter reading is \(3.0\,V\).
(c) State the reading of the ammeter, in mA.
(d) Calculate the emf of the cell.

Most-appropriate topic codes (IB Physics):

• Topic B.5: Electric current and circuits — parts (a), (b), (c) and (d)
▶️ Answer/Explanation
Detailed solution

(a)
From the graph for P at \(10\,V\), \(I = 200\,mA = 0.20\,A\).
\(R = \frac{V}{I} = \frac{10}{0.20} = 50\,\Omega\).

(b)
The resistance increases as the current increases, as shown by the decreasing gradient of the I–V graph.

(c)
The ammeter is in series with Q. From the graph for Q at \(V = 3.0\,V\), the current is \(120\,mA\).

(d)
Current in the series circuit \(I = 0.12\,A\).
Potential difference across P: \(V_{P} = IR_{P} = 0.12 \times 50 = 6.0\,V\).
\(\text{emf} = V_{P} + V_{Q} = 6.0 + 3.0 = 9.0\,V\).

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