Lab 3 - Capacitors

Lab 3 - Capacitors - PHY134 - Classical Physics II...

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PHY134 - Classical Physics II Laboratory Capacitors In this experiment we will determine the capacitance of an unknown capacitor by observing the change in potential difference between its plates when, after being initially charged, it is connected in parallel with a known capacitor. We will also study the behavior of capacitors connected in series. Equipment Oscilloscope, Unknown capacitor, Decade capacitance box with 1 μ F steps, Double-pole double-throw switch, Dry cell. Method In Part I, a capacitor C 1 is charged to potential V 0 by connecting it across a dry cell. The cell is disconnected and then an initially uncharged capacitor C 2 is connected in parallel with C 1 . Charge will flow from C 1 to C 2 until the potentials across the capacitors equalize. The voltage across the parallel combination is given by: V = V 0 C 1 /( C 1 + C 2 ) (1) Q1. Derive equation (1) Rearranging equation (1) gives: V 0 / V = C 2 / C 1 + 1 (2) C 2 is an adjustable capacitor. As C 2 is changed, the final voltage V will vary according to equations (1) and (2). In Part II, a similar procedure is applied to capacitors connected in series. Procedure 1. Capacitors in Parallel Connect the circuit as shown in Figure 1. C 1 is a fixed capacitor whose capacitance is to be measured. C 2 is a decade capacitance box with variable capacitance from 0 to 10 microfarads ( μ F) in steps of 1 μ F. With the switch in position (1) (as shown), C 2 is discharged and C 1 is charged to the voltage of the battery V 0 . This voltage can be read on the oscilloscope. With the switch in position (2), the battery is disconnected,
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Lab 3 - Capacitors - PHY134 - Classical Physics II...

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