The student closes the switch. Fig. 1.2 shows the current $I_L$ and potential difference $V_L$ readings. Write down the values shown.
After the readings have been recorded, the student opens the switch. Suggest why this is done.
Use the equation $R = \frac{V}{I}$ to calculate the lamp resistance $R_L$. Give the answer to 2 significant figures.
The student changes the circuit so that a $10\,\Omega$ resistor is connected in series with the lamp, and the voltmeter measures the potential difference across the resistor-lamp combination. In the space below, draw the updated circuit with the resistor included.
The voltmeter reading stays the same. Fig. 1.3 displays the new ammeter reading; this is current $I_C$. Record $I_C$. Then use the equation in (a)(iii) to determine the resistance $R_C$ of the lamp and the resistor in series.
The theory gives $R_L = R_C - 10$ for the new circuit. Calculate the lamp resistance $R_L$.
State how the lamp’s brightness differs in the new circuit from the circuit shown in Fig. 1.1, and explain the reason.