A variable resistor is fitted to regulate the current in a circuit, as shown in Fig. 5.1. It is connected in series with a $12\,\text{V}$ power supply of negligible internal resistance, an ammeter and a $6.0\,\Omega$ resistor. The resistance $R$ of the variable resistor may be changed from $0$ to $12\,\Omega$.
The largest current that can occur in the circuit is $2.0\,\text{A}$. Calculate the smallest current.
On Fig. 5.2, sketch the way in which current $I_1$ varies with $R$ in the circuit.
The variable resistor in (a) is now arranged as a potential divider, as shown in Fig. 5.3. Calculate the greatest possible and smallest possible current $I_2$ in the ammeter.
On Fig. 5.4, sketch the $I$-$V$ characteristic for a filament lamp.
The resistor of resistance $6.0\,\Omega$ is replaced by a filament lamp in the circuits of Fig. 5.1 and Fig. 5.3. State an advantage of choosing the circuit of Fig. 5.3 rather than the circuit of Fig. 5.1 when using the circuits to alter the brightness of the filament lamp.
The resistor of resistance $6.0\,\Omega$ is replaced by a filament lamp in the circuits of Fig. 5.1 and Fig. 5.3. State an advantage of selecting the circuit of Fig. 5.3, compared with the circuit of Fig. 5.1, when the circuits are used to alter the brightness of the filament lamp.