Physics 1082
Lab #8 Faraday’s Law
Eric Wheelock
Date Performed: 4/26/2025
Mahmoud Eid, PhD
Abstract
This experiment investigated the behavior of a simple parallel circuit consisting of
a resistor and a light bulb, and then expanded to include the effects of self-inductance
using an inductor. Using a 50 V battery, a switch, and two resistors in parallel (one
representing a light bulb), we first observed voltage and current changes when the
switch was toggled. In the second part, a 5 H inductor was added in series with the lowresistance branch to simulate motor coil inductance. The goal was to observe and
quantify the induced emf and changes in current and voltage behavior due to selfinduction. The results confirmed the prediction that self-inductance causes significant
delay and overshoot in current and voltage when switching.
Circuit one with 2 parallel resistors.
Circuit 2 with a resistor in parallel with an inductor.
Data
Scenario
Prediction:
Prediction:
Observation:
Observation:
Voltage
Current
Voltage Across
Current
Across
Through Bulb
Switch
Through Bulb
Switch
Switch
50 V
0A
50 V
0A
0V
0.5 A
0V
0.5 A
50 V
0A
Spike > 50 V
0A
Open (No
Inductor)
Switch
Closed (No
Inductor)
Switch
Open (With
temporarily, then
Inductor)
50 V steady
Switch
Closed
(With
Inductor)
0V
Gradual rise
Voltage drops to
Current rises
to 0.5 A
0 V slowly
slowly to 0.5 A
Results
Without Inductor:
When the switch was open, the full battery voltage (50 V) was measured across
the switch and no current flowed through the bulb.
When the switch was closed, the voltage across the switch dropped to nearly 0 V
immediately, and current through the bulb jumped instantly to its steady-state value
(approximately 0.5 A).
With Inductor Added:
When the switch was closed, the current through the bulb rose gradually rather
than instantly, indicating the inductor opposed sudden changes in current (selfinductance effect).
Upon opening the switch, the voltage across the switch momentarily spiked to a
value greater than the supply voltage (greater than 50 V), demonstrating the presence
of a large induced emf due to the rapid decrease in current through the inductor.
Conclusion
The experiment confirmed the fundamental principles of electromagnetic
induction in circuits containing inductance. Without an inductor, the voltage and current
responded almost instantaneously to the closing or opening of the switch. When the 5 H
inductor was added, a significant delay in current rise and fall was observed, along with
a noticeable induced emf spike when the switch was opened. This behavior models how
real-world devices like electric motors generate large back-emfs during sudden
operational changes. The experimental results aligned with theoretical expectations,
demonstrating how inductors resist changes in current and can cause voltages much
larger than the applied voltage during rapid switching events.