State how a voltmeter must be connected in a circuit to measure the potential difference across the lamp $L$.

In Circuit 1, the student reads the analog voltmeter and ammeter.

• The analog voltmeter has a range of $0$ to $10V$ with minor divisions every $0.2V$. The pointer points to three small divisions past the $4V$ mark.
• The analog ammeter has a range of $0$ to $2.0A$ with minor divisions every $0.05A$. The pointer points to one small division before the $0.5A$ mark.

State the values of: (i) the potential difference $V_1$ across the lamp, including its correct unit. (ii) the current $I_1$ through the lamp, including its correct unit.

In Circuit 2, the circuit is rearranged so that the same lamp $L$ is dimmer. The electrical readings are:

• Potential difference $V_2=1.8V$
• Current $I_2=0.24A$

(i) Calculate the resistance of lamp $L$ in Circuit 1 ($R_1$) and in Circuit 2 ($R_2$) using the equation $R=\frac{V}{I}$. Give your answers to 2 or 3 significant figures. (ii) State the standard SI symbols used for potential difference, current, and resistance in column headings (e.g., of the form $Quantity/Unit$).

A classmate suggests that since the same physical lamp $L$ is used in both circuits, its electrical resistance should be identical in both experiments. State whether your calculated values of $R_1$ and $R_2$ support this idea, and justify your answer by referring to the results.

A physics theory suggests that the resistance of a metal filament in a lamp increases as its operating temperature increases. Describe whether the observations (Circuit 1 lamp is bright, Circuit 2 lamp is dim) support this theory.

Describe how a variable resistor should be connected in a circuit containing a power supply and a lamp to vary the current continuously, and describe its standard schematic symbol.