RC, LR, AND LC CIRCUIT LABS Peggy Bertrand Oak Ridge High School Oak Ridge, TN pbertrand@ortn.edu

RC, LR, AND LC CIRCUIT LABSPeggy Bertrand

Oak Ridge High School

Oak Ridge, TN

pbertrand@ortn.edu

College Board ObjectivesB C

RC CIRCUITS

RC Circuit Lab Equipment

Low tech

• Capacitors• 100mF to 300 mF

• Resistors• 15,000 W or higher

• D-Cells• Knife switch (spdt)• Connecting wires• Voltmeter• Kid with a pencil

High tech

• Add a Pasco or Vernier system with a voltage probe

RC Circuit – low tech

$1.00

$2.00

$3.00 $5.00

<$1.00$15.00

RC Circuit – high tech

$1.00

$2.00

$3.00$5.00

<$1.00$350 - $425

RC Circuit Lab – student instructions

Build an RC circuit that can undergo charge and discharge cycles with a flip of the switch.

Use capacitors of between 100 mF and 300 mF, and resistors of between 10,000 W

and 100,000 W.

Collect voltage data over the resistor and over the capacitor for the charge and the

discharge cycles and produce graphs of these data.

Compare the predicted and graphically determined time constants for your circuit .

Repeat for a second circuit with a different capacitive time constant.

Your report must include:

• Your graphs.

• Circuit diagram

• Graphically-determined capacitive time constants.

• Predicted capacitive time constants.

• Comparison of time constant values.

Circuit setup

A

B

V

V

RC Circuit Charge and Discharge Data

This circuit was built with a 15000 W resistor and a 1000 mF capacitor.Calculated time constant: 15 s. Graphical time constant: 14 s.

RC

Circuit Q

uestion

LR CIRCUITS

LR Circuit Lab

OR

LR Circuit Setup

V

A

LR Circuit Results

LR Circuit Results

Alternative Student-Built Circuit

V

V

RC

and LR C

ircuit Question

LC CIRCUITS

LC Circuit Lab Equipment

OR

AND

LC Circuit – Instructions to Students• Build an LC circuit with an inductor, capacitor, DC power

supply, and a single-pull double-throw switch. • The switch should be used to charge the capacitor using

the DC voltage source when it is in one position, and to discharge the capacitor through the inductor when it is in the other position.

• There is resistance in your inductor that will damp the oscillations, so don’t add any additional resistance! (You are really building an LRC Circuit)

• Rapidly sample the voltage across the capacitor to obtain a damped oscillator curve.

• Compare the period you obtain to the predicted period.

Circuit Setup• Capacitor charges when

switch is in position A.• When moved to position B,

an LRC circuit undergoes damped oscillation with a period predicted by:

B

A

V

LCT 2

C

e

LC (well, really LRC) Circuit Results

Data taken with Pasco Science Workshop 750, sampled at 5000 Hz

LC Circuit Question

Thank you for your attention…