Ohm's Law: Circuits, Bulbs and Buzzers (page 2)
Series and parallel circuits
- Attach each of the two ends of a Christmas tree bulb (or a low-voltage bulb in a socket) across the power supply. (This means one of the wires attached to the bulb goes to the positive terminal and the other end goes to the negative lead.)
- Connect three (or more) bulbs in series. Compare the brightness of these bulbs with the brightness of a single bulb.
- Connect three bulbs in parallel and compare with the brightness of bulbs in a series and a single bulb.
Measuring the circuit
- Repeat the previous set of measurements, but this time, include an ammeter in series with the circuit and a voltmeter in parallel with the circuit, as shown in Figure 100-2. It helps with the comparison if you keep the voltage constant throughout these measurements and compare the current flowing in the circuits.
- Compare the current flowing in each the situations.
- Apply Ohm's law (in the form R = V/I) to find the resistance of each of the circuits you measured.
Current will flow in a circuit if a continuous path exists from the positive terminal of the power supply through all components of the circuit, and then back to the negative terminal of the power supply.
Components in series reduce the current that can flow by effectively adding resistance to the circuit.
Components in parallel result in increased current flowing through the circuit. The resistance of the overall circuit is reduced when components are added in parallel.
Why It Works
When components are added in series, the voltage is distributed over all the components. As a result, less current is able to flow.
When components are added in parallel, alternate paths are provided for the current to flow back to the battery. For a given voltage, the push from the battery is able to force more current through the larger number of paths.
Other Things to Try
A next logical step is to create and test more complex networks of resistors. The following shows some examples. These can be analyzed using the following principles:
- Resistors in series simply add: Rseries = R1 + R2
- Resistors in parallel add in a more complex fashion. Resistors in parallel can be thought of as one single equivalent resistance given by: 1/Rparallel = 1/R1 + 1/R2 + …
- These circuits can then be simplified by combining series and parallel circuits, and then applying Ohm's law in its various forms (V = RI, R = VI, and I = V/R).
Ohm's law determines how much current (or amps) flows through a circuit. For a given resistance (ohms), the greater the voltage, the greater the current.
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