Download Ohm`s Law

Demonstration: Ohms Law for Serial and Parallel Circuits
Leonard Freise
Bruce Dillon
Lane Matheson
Objective: Introduce a visual demonstration of Ohm’s Law.
Lights
Batteries
Parallel
Series
Equipment:
 2 –Lights
 Power Source
 Wires with Alligator clamps
 Multimeter
Discussion:
Demonstrate set-up of a circuit with one light bulb. Ask students to notice the
brightness of the bulb. Place a second bulb in parallel with the first one. Note that
the brightness of the bulbs stays the same, but the current increases. Next,
rearrange the bulbs in series. Note that the brightness of the bulbs decreases
compared to before, but the current is the same as when there was only one bulb in
the circuit. The light bulb is an example of a resistor. The resistance of any
material is measured by the relationship R = V/I where V is the potential
difference measured in volts and I is the current measured in amps. Resistance is
measured in Ohms, , which is equivalent to volts/amps.
For many materials, the resistance is constant over a wide range of voltages and
currents. Light bulbs are designed to have increasing resistance as voltage is
increased, so the light bulbs will not demonstrate the concept of constant
resistance. The exercise that accompanies this demo uses resistors instead of bulbs
to allow students to verify Ohm’s Law.
Questions:
1. What would you expect to happen to the brightness of the bulbs if we placed
a. Three bulbs in parallel?
b. Three bulbs in series?
2. What would you expect to happen to the current if we placed
a. Three bulbs in parallel?
b. Three bulbs in series?