IB Physics HL B.5.14 EMF and Internal Resistance Question Bank

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

Exam points

Derive ε = V + Ir and use current–voltage data to obtain emf and internal resistance.
Compare load power with power lost in internal resistance and identify the maximum-power condition.
Analyse cells in series or parallel when emf, internal resistance and terminal voltage change.

[Maximum number: 4]

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 $=\frac{3.00}{5.00}=0.600 \mathrm{~A}$ ;
$R=\frac{9.00}{0.600}=15.0 \Omega$ ;

All question bank results loaded

B.5.14—Emf and internal resistance question 1