A student investigates an electric circuit. The figure below shows the student’s circuit.
Describe the purpose of the variable resistor in the figure.
The student uses cells with an electromotive force (e.m.f.) of 
. Determine the number of cells needed for the 
battery in the figure.
The student connects another component to measure the potential difference (p.d.) across the heater. On the figure draw the electrical symbol and connections for this component.
.
