A student investigates the current in a coil and a resistor connected in series, as shown in Fig. 1.1. [Figure 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 = KN²A / 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.