Define the ohm in terms of V and A.
A wire has a resistance of $1.8\,\Omega$. Its uniform cross-sectional area is $0.38\,\text{mm}^2$ and it is made from a metal with resistivity $9.6 \times 10^{-7}\,\Omega\,\text{m}$. Calculate the length of the wire.
The battery P has an electromotive force (e.m.f.) of $1.2\,\text{V}$ and negligible internal resistance. Explain, in terms of energy, why the potential difference (p.d.) across resistor X is smaller than the e.m.f. of the battery.
Calculate the p.d. across resistor X.
A second battery Q with e.m.f. $1.2\,\text{V}$ and negligible internal resistance is now added to the circuit of Fig. 5.1 to make the revised circuit shown in Fig. 5.2. State whether adding battery Q makes the current in resistor X decrease, increase or stay the same.
State whether the addition of battery Q causes the current in battery P to decrease, increase or stay the same.
The circuit in Fig. 5.2 is changed to make the new circuit shown in Fig. 5.3. Calculate the total resistance of the two resistors connected in parallel.
Calculate the current in resistor Y.