Physics 9702/51 — May/June 2021

A student investigates the current in a coil and a resistor connected in series, as shown in Fig. 1.1.

The student connects a high-voltage d.c. power supply and a switch across the series combination.

When the switch is closed, it takes time $t$ for the current in the resistor of resistance $R$ to reach a maximum value. The time $t$ is a few milliseconds.

There are a number of different unmarked resistors available.

It is suggested that the relationship between $t$ and $R$ is

$$t = \frac{KN^2A}{LR}$$

where $N$ is the number of turns of wire on the coil, $A$ is the cross-sectional area of the coil, $L$ is the length of the coil and $K$ is a constant.

Design a laboratory experiment to test the relationship between $t$ and $R$.
Explain how your results could be used to determine a value for $K$.

You should draw a diagram, on page 3, showing the arrangement of your equipment. In your account you should pay particular attention to:

● the procedure to be followed
● the measurements to be taken
● the control of variables
● the analysis of the data
● any safety precautions to be taken.