The results of an experiment to determine the e.m.f. E and internal resistance r of a power supply are shown in Table. Plot a suitable graph and use it to find E and r.

V / V	1.43	1.33	1.18	1.10	0.98
I / A	0.10	0.30	0.60	0.75	1.00

 

A car battery has an e.m.f. of $12 \mathrm{V}$ and an internal resistance of $0.04\Omega$. The starter motor draws a current of $100 \mathrm{A}$.

Calculate the terminal p.d. of the battery when the starter motor is in operation.

Design a circuit using the thermistor in Figure that uses a cell of $10 \mathrm{V}$ and produces an output voltage of $5 \mathrm{V}$ at $50°\mathrm{C}$. Explain whether the voltage output of your circuit increases or decreases as the temperature rises.

Variation of resistance with temperature.

To make a potentiometer, a driver cell of e.m.f. $4.0 \mathrm{V}$ is connected across a $1.00 \mathrm{m}$ length of resistance wire.

(a) What is the potential difference across each $1 \mathrm{cm}$ length of the wire? What length of wire has a p.d. of $1.0 \mathrm{V}$ across it?

To make a potentiometer, a driver cell of e.m.f. $4.0 \mathrm{V}$ is connected across a $1.00 \mathrm{m}$ length of resistance wire.

(b) A cell of unknown e.m.f. $\mathrm{E}$ is connected to the potentiometer and the balance point is found at a distance of $37.0 \mathrm{cm}$ from the end of the wire to which the galvanometer is connected. Estimate the value of $\mathrm{E}$. Explain why this can only be an estimate.

To make a potentiometer, a driver cell of e.m.f. $4.0 \mathrm{V}$ is connected across a $1.00 \mathrm{m}$ length of resistance wire.

(c) A standard cell of e.m.f. $1.230 \mathrm{V}$ gives a balance length of $31.2 \mathrm{cm}.$ Use this value to obtain a more accurate value for $\mathrm{E}$.

A resistor of resistance $6.0\Omega$ and a second resistor of resistance $3.0\Omega$ are connected in parallel across a battery of e.m.f. $4.5 \mathrm{V}$ and internal resistance $0.50\Omega$. What is the current in the battery?

(A) $0.47 \mathrm{A}$

(B) $1.8 \mathrm{A}$

(C) $3.0 \mathrm{A}$

(D) $11 \mathrm{A}$

A single cell of e.m.f. $1.5 \mathrm{V}$ is connected across a $0.30 \Omega$ resistor. The current in the circuit is $2.5 \mathrm{A}$.

Calculate the terminal p.d. and explain why it is not equal to the e.m.f. of the cell.

A student is asked to compare the e.m.f.s of a standard cell and a test cell. He sets up the circuit shown using the test cell.

(a) (i) Explain why he is unable to find a balance point and state the change he must make in order to achieve balance.