capacitor discharge

The voltage and current in a circuit change when a capacitor charges and discharges. Computer sensors can measure these changes and software can plot a graph as fast as this happens. Also, the effect of changing the capacitor and resistor in the circuit can easily be explored.

What you need

A 1000 mF capacitor, 1kW resistor, power supply, switch, leads, voltage and current sensors, interface. You may need to ‘bias’ the voltage to get your readings on screen.

Setting up

Connect up the circuit.
Connect the current sensor to the interface and the voltage sensor to another socket. If the sensors are adjustable, set a 100mA range on the current sensor and a 10V range on the voltage sensor.
Run your sensing software. Your system may recognise the sensors automatically, otherwise you will need to set them up yourself. Do a short test run to see that your readings are within range and will be displayed on the screen.
Set your sensing software to record for 1 minute. Charge the capacitor and when it is charged, move the switch to allow it to discharge.

Describe the graph you see.
What does the graph tell you about the way a capacitor discharges?
Make changes to the values of the capacitor and the resistor and discuss the factors that affect the way a capacitor discharges.

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