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Lecture Demonstrations Laboratory

Physics Rm. 202

(434) 924-6800

The Demonstrations Manual

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Electric Fields And Potential
Current and Resistance
Electromotive Force And Current
DC Circuits
Ohm's Law
Resistivity of a Pencil
Resistive Heating of Nichrome Wire
Blowing a Fuse
Wheatstone Bridge
Wheatstone Bridge II
Circuit Analysis
RC Circuit w/ Function Generator
RC Circuit w/ Battery
RC Time Constant (DECAY)
Telephone model as simple DC circuit
Magnetic Materials
Complex Circuits
Semiconductors And Tubes
Transmission Lines and Antennas

RC Circuit w/ Function Generator


A square wave charges and discharges a capacitor and the charging time is observed on the oscilloscope. To demonstrate the time constant of an RC circuit and its dependence on R and C.


Connect R and C in series and use the PASCO generator's square waves as a signal source. Start with 100 Ω resistor and 0.47 μF capacitor and display the voltage across the capacitor (see 2nd picture). Vary the values of C and R (provided) to show the change of the time constant. Show the voltage across the resistor to demonstrate the current dependence in the circuit (see 3rd picture). A schematic of the set up is shown below (4th picture).


New Tektronix DPO 3014 Scope Setup:
  • There are two Instek GDP-025 differential probes attached to CH1 and CH2.
  • Scope has VGA output whose signal can be projected onto screen.
Old HP 1200A Scope Setup:
  • Use differential input oscilloscope to display both the charge and the current dependence.
  • A camera pointing at the scope's screen is available for the use in any of the rooms.
To reduce the time constant two resistors could be quickly put in parallel by stacking them on top of each other.


  • Oscilloscope
  • Connecting Wires
  • Large Bread Board
  • Resistor - Capacitor Substitution Box
  • Wave Generator