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1Experimental Planning SafetyHard15 marks

A capacitor is connected to a reed switch, a d.c. power supply of negligible internal resistance and a resistor, as shown in Figure 1.1.

Figure 1.1, a circuit diagram: a d.c. supply, drawn as two open-circle terminals at the left, has its top terminal wired to one fixed contact of a reed switch (drawn as a box); inside the box a two-way switch S has a moving arm that can touch either this contact (solid line) or a second contact shown dashed, which is wired from the top of the box to a resistor drawn as a rectangle on the far right; two small square terminals F and G, for the alternating-current drive signal, are mounted straddling the box's right-hand edge; switch S's arm leads down out of the box to a capacitor, drawn as two parallel plates, whose lower plate joins a common bottom rail (marked with a filled dot) that returns to both the d.c. supply's other terminal and the resistor's other terminal

The reed switch is a device that contains a two-way switch S that connects the capacitor either to the d.c. supply or to the resistor. An alternating current is supplied to terminals F and G of the reed switch. This causes switch S to vibrate. The frequency

f

of switch S is the same as the frequency of the alternating current. For half of one cycle of the alternating current, the capacitor is charged from the d.c. supply. For the other half of the cycle, the capacitor discharges through the resistor. The mean current in the resistor is

I

. The capacitor is created from two circular metal plates in air. The plates each have area

A

. The plates are separated by a small distance

h

. It is suggested that

I

is related to

h

by the relationship

\frac{K A}{h} = \frac{I}{f E}

where

E

is the electromotive force (e.m.f.) of the d.c. supply and

K

is a constant. Plan a laboratory experiment to test the relationship between

I

and

h

. Draw a diagram showing the arrangement of your equipment. Explain how the results could be used to determine a value for

K

. In your plan, you should include:

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

Draw with the mouse or a finger.

May/June 2026 Paper 52

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