RC, LR, AND LC
CIRCUIT LABS
Peggy Bertrand
Oak Ridge High School
Oak Ridge, TN
pbertrand@ortn.edu
College Board Objectives
B
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
$3.00
$5.00
$2.00
$1.00
$15.00
<$1.00
RC Circuit – high tech
$5.00
$3.00
$2.00
$1.00
$350 - $425
<$1.00
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
B
A
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 Question
LR CIRCUITS
LR Circuit Lab
LR Circuit Setup
LR Circuit Results
LR Circuit Results
Alternative Student-Built Circuit
RC and LR Circuit Question
LC CIRCUITS
LC Circuit Lab Equipment
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:
A
C
B
e
T  2 LC
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…