Electricity & Magnetism: Ohm's Law
Explore the relationship between current and voltage for a simple DC circuit with a resistor in series with a capacitor. Do the same for a light bulb in series with a capacitor. Compare the plot of voltage versus current for the light bulb to the plot for the resistor.
Students will discover that the slope of their voltage/current graph is the resistance in the circuit (Ohm's Law).
Lab Summary
Students will use the Voltage/Current Sensor to investigate the relationship between current, voltage, and resistance in a direct current (DC) circuit.
Students will measure voltage and current for a circuit with a resistor in series with a capacitor as the capacitor is discharged through the resistor. They will repeat the measurement with a different resistor. They will examine the slope of a plot of voltage versus current and compare the slope to the resistance of the circuit.
Students will measure the voltage and current for a circuit with a light bulb in series with a capacitor as the capacitor is discharged through the light bulb. They will compare the plot of voltage versus current for the light bulb to the plot for the resistors.
Theory
Ohm's Law states that as voltage increases, so does current. The relationship is summarized as V = IR where V is voltage, I is current and R is resistance. Many objects follow this linear formula and use of the Voltage/Current Sensor and two resistors of different values will verify that fact. However, some objects (such as a light bulb) do not follow Ohm's Law in a strictly linear fashion.
Downloads
- Computer-based lab (PDF, 554 KB) (554 KB, .pdf)
(student version)
- Xplorer GLX-based lab (PDF, 592 KB) (592 KB, .pdf)
(student version)
Method
Use a Voltage-Current Sensor to measure the voltage across a resistor and the current through the resistor as the voltage is increased. Examine the graph of voltage versus current and compare the slope of the graph to the resistance of the resistor.
Here's What You Need
U.S. Educator prices shown.
Required for computer-based lab: (See lab download for Xplorer GLX-based lab requirements, which may differ)
Probeware
PASPORT Voltage-Current Sensor (PS-2115) - $99
Allows students to safely measure voltage and current simultaneously without overloading the sensor. For use with PASPORT Interfaces.
Xplorer GLX (PS-2002) - $349
The Xplorer GLX is a data collection, graphing, and analysis tool designed for science students and educators.
Other Products
Charge/Discharge Circuit (EM-8678) - $135
Observe and measure the behavior of DC circuits with batteries, capacitors, light bulbs, and resistors.
Banana Plug Cord-Red (5 Pack) (SE-9750) - $20
Heavy insulation patch cords are convenient, durable and inexpensive. Set of 5 red assembled cords.
Lab Manual
The computer-based activity is included in Explorations in Physics (PS-2810). The Xplorer GLX-based lab is included in Physics with the Xplorer GLX (PS-2826). Both manuals are complete with Teacher Information pages, student instructions and handouts, and sample data.
For your convenience, we offer bundles which provide the probeware for the
activities in the manual. For more, please see:
Computer-based
Physics Lab Manual and Bundles
Xplorer
GLX-based Physics Lab Manual and Bundles
