Physics Demo Number: 071

Approximate Run Time: 10 min

RC Time Constant

Demo Description

Use a capacitor, battery, multimeter, resistor to show both an RC rise in voltage and an RC decay.

 

Scientific Principles

  • RC rise in voltage

  • RC Decay

Equipment

  • 20000 micro farad capacitor

  • Battery

  • Large Digital Multimeter ( Note that this meter is self-contained and has a big enough digital l.e.d readout to see throughout the lecture hall.)

  • A resistor (R on gray terminal block ) and Arc-Conductor- Tubes ( 1, and 7 ) for rise time, and Arc 8 for decay.

  • Cart [A-B]  houses equipment dedicated to to several experiments.

 



Equipment Location

  • The 20000 micro farad capacitor and battery are both permanently attached to Cart [A-B].

  • Cart [A-B] itself lives against the library wall at the end of the [A-B] columns row.

  • The large digital multimeter is in Large Kit(071) on [B-2-2].

  • The resistor and Arc-Tubes live on the lower shelves of Cart[A-B] which lives against the wall at the end of the aisle between the A and B columns.

 

Instructions

The first photo shows the configuration of the two Arcs ( 1 and 7 which are yellow and orange respectively) and the resistor R.

The photo captured the system at the end of the R-C rise .

Notice that only Terminals 1,2,7, and 8 are utilized for the R-C rise time demo, and only Terminals 1and 2 are used for the R-C decay demo.

Notice further that we are viewing the setup from the black board or instructors side. (If the instructor stands on the front side, he/she will be blocking the view of many students. )

The meter has been faced toward the instructor or camera for clarity in the description. In actual use in the classroom the meter faces the students, and the instructor may read the small back-face digital readout on the meter.

A list matching Arcs with their terminal connection numbers is taped to the cart on the front-right in the photo.

One may remove Arcs 1 and 7 and put Arc 8 in place, as seen in the next photo , to demonstrate R-C decay.




Attempts at utilizing the bulb hanging on the cart frame for showing R-C  time constants are strongly not recommended. 








Writeup created by David A. Burba
Copyright © 2013, Vanderbilt University.   All Rights Reserved.