RC Circuits

• Study the charging and discharging of a capacitor, and observe how the rate depends on the values of capacitance and resistance in the circuit.
• Become familiar with the use of the oscilloscope, probably the most important research instrument for studying electrical circuits.

Equipment: "Water battery" and 27000 microfarad capacitor, miniature lamp and carbon resistor combinations, digital multimeter for potential difference Oscilloscope, function generator, and resistor-capacitor combinations

Predict/Test:

• Discharge a capacitor through a two-resistor combination. How does the time required for discharge depend on the resistance?
• Charge and discharge a two-capacitor combination through a resisitor. How does the time required depend on the capacitance?

Qualitative: Discharge a capacitor through a miniature lamp. Does the potential difference fall exponentially? Record potential difference versus time when you control charging and discharging of a capacitor. Compare to the oscilloscope trace when a function generator controls charging and discharging of a capacitor.

Quantitative:

• What is the total resistance of two resistors in series? ...in parallel?
• Determine the resistance of the source of emf.

"Real World" Applications:

• Strobe lamps, flashing warning lights, and camera flashlamps
• Digital clocks and watches

"Toys Table:"

• The "Oxford Flasher"
• Join Hands - resistance of students in series
• Invent a triangle wave generator!

Updated 29 May 2002

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