Electric current is the movement of charge carriers. The charge carried by them is quantised. Explain what is meant by quantised.
A battery with electromotive force (e.m.f.) $9.0\,\text{V}$ and internal resistance $0.25\,\Omega$ is joined in series with two identical resistors X and a resistor Y, as shown in Fig. 7.1. Each X has resistance $0.15\,\Omega$ and Y has resistance $2.7\,\Omega$. Show that the current in the circuit is $2.8\,\text{A}$.
Calculate the potential difference across the battery.
Each resistor X in the circuit in (b) is made from a wire with cross-sectional area of $2.5\,\text{mm}^2$. The number of free electrons per unit volume in the wire is $8.5 \times 10^{29}\,\text{m}^{-3}$. Calculate the average drift speed of the electrons in X.
The two resistors X are replaced by two resistors Z made of the same material and length but with half the diameter. Describe and explain the difference between the average drift speed in Z and that in X.