RC Circuits

In this investigation, you will compare the time, τ, it takes to charge a capacitor in an RC circuit with the stated time for the capacitor and resistor used. This is a student-designed investigation where the voltage, capacitor and resistor can be selected based on the equipment available.

You will need the following equipment:

• • power supply or battery (V0)

  • 2 switches

  • resistor (R)

  • capacitor (C)

  • voltmeter.

Set up the circuit shown below. Connect the voltmeter across the resistor.

Calculate the time interval, τ, for the equipment you have chosen. Close switch 1 and note the readings on the voltmeter.

Complete the following table.

Construct a graph like the one below for your results and find the time, τ, taken for the voltage across the capacitor to

reach 63% of the supply voltage.

• 1. How did your results compare with the stated quantity for the capacitor and resistor used?

  2. Why shouldn’t you measure the voltage directly across the capacitor with the voltmeter?

  3. What can you change in your circuit to increase the time taken to charge the capacitor?

  4. What do you expect would happen if you opened switch 1 and closed switch 2? Check your prediction.