Series & Parallel Circuits (OCR A Level Physics)

Fig. 18.1

The cell has e.m.f. 1.5 V. The cell and the variable power supply both have negligible internal resistance.

Calculate the current I in the 33 Ω resistor.

I = ........................................... A [3]

Describe the effect on the current I in the 33 Ω resistor.

[2]

Fig. 18.2 shows the data points plotted by the students on a graph of P (y-axis) against R (x-axis).

Fig. 18.2

The group of students know that maximum power is dissipated in the variable resistor when R is equal to the internal resistance r of the cell.

Describe, with the help of a suitable circuit diagram, how the students may have determined P and R. Use Fig. 18.2 to estimate the internal resistance r of the cell and discuss any limitations of the data plotted by the group.

[6]