On Fig. 2.1, add the symbol for a voltmeter so that it measures the potential difference $V_{XY}$ across the $270\,\Omega$ resistor.
Enter $V_{XY}$ in Table 2.1.
Calculate the value of $(V_{XY}+V_{YZ})$ for the $270\,\Omega$ resistor, and write the result in Table 2.1.
The current $I$ in the circuit can be worked out using the equation $I = \frac{V_{XY}}{R}$ where $R = 270\,\Omega$. Calculate $I$. Enter your answer in Table 2.1.
The resistance $R_{LED}$ of the LED can be found using the equation $R_{LED} = \frac{V_{YZ}}{I}$. Calculate $R_{LED}$. Enter your answer in Table 2.1.
Calculate $V_{XY}$ and enter your answer in Table 2.1 on page 6.
Describe how the change in current affects $(V_{XY}+V_{YZ})$.
Describe how the change in current affects $R_{LED}$.
Suggest the mistake the student made while assembling the circuit.
Name and draw the symbol of a single device that can be used to vary the current in the circuit without needing to connect different resistors across terminals X and Y.