IB Physics HL B 5 14 Emf and Internal Resistance Questions

Practise IB Physics HL B.5.14 by modelling real cells, extracting internal resistance from data, and analysing power and energy transfer.

Exam points

Calculate emf, terminal potential difference or internal resistance from linked circuit data using ε = I(R + r) and V = ε − Ir.
Analyse V–I and transformed graph data to obtain emf and internal resistance from intercepts, gradients or extrapolation.
Plan or evaluate an internal-resistance investigation, including circuit arrangement, repeated readings, line-of-best-fit gradients and heating effects.
Relate load resistance to current, terminal potential difference, internal power loss and maximum power transfer in a real cell.
Model series and parallel combinations of cells by combining emf and internal resistance before calculating circuit current or terminal potential difference.

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Study B.5.14—Emf and internal resistance conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

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This question is in two parts

The plates in (c) are replaced by a cell that has an emf of 12.0 V and internal resistance $5.00 \Omega$ . A resistor of resistance R is connected in series with the cell. The energy transferred by the cell to an electron as it moves through the resistor is $1.44 \times 10^{-18} \mathrm{~J}$ .

Show that the value of R is $15.0 \Omega$ .

pd across $R=\frac{1.44 \times 10^{-18}}{1.6 \times 10^{-19}}=9.00 \mathrm{~V}$ ;
pd across internal resistance $=12.0-9.00=3.00 \mathrm{~V}$ ;
current in circuit $=\frac{3.00}{5.00}=0.600 \mathrm{~A}$ ;
$R=\frac{9.00}{0.600}=15.0 \Omega$ ;

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IB Physics HL B 5 14 Emf and Internal Resistance Questions question 1