07/09/02 Lab Exercise
Bears: Rebecca Morales, Bill Davis, Jennie Lynch
Electricity: Series and Parallel
Objective:
Our objective is to gain understanding of the relationship between Voltage (volts), Current (amperes), and Resistance (ohms), Ohm’s Law, and how these are used to explain what happens in series and parallel circuits.
Equipment:
3 AC/CD Power Supplies
2 Light sockets
3 light bulbs ( 2 of the same wattage, 1 different)
8 wires
1 switch
Procedure:
1. Connect one light fixture to the power source. Make observations.
(These are theoretical values)
2. Change the light bulb to one of different wattage. Observe the difference.
3. Connect the 3 power sources in series.
4. Connect the 2 light fixtures (both with same wattage bulb) in series.
5. Before you complete the circuit, explain what you think will happen.
6. Connect the lights in parallel. Once again, explain what you expect will happen.
Discussion:
Using the switch in the circuit helps to demonstrate the potential which is realized when the circuit is closed. By comparing the output of the two different wattage bulbs you can discuss the relationship between resistance and power. Connecting the power sources in series, lets you combine the total voltage of the three:
Once again, the voltage and amperage here are theoretical values, but it is important that the students do the math to understand how each of these things effect each other. If you know the wattage of the bulbs and the voltage being generated you can calculate the resistance of the bulbs using the formula for power:
You should be able to predict from the calculations if the bulbs will be brighter when in series or in parallel.
Questions:
1.Which bulb will burn brighter, the larger wattage or the smaller wattage and why?
2. When the bulbs are in series, would you expect them to burn brighter or less bright?
3. Will each bulb have the same brightness?
4. When the bulbs are in parallel, how many amps are going through each bulb?
5. So what do you expect will happen to the brightness?
6. Will each bulb have the same brightness?