http://www.ck12.org Chapter 5. Energy
5.70 Ohm’s Law
- Explain Ohm’s law.
- Use Ohm’s law to calculate current from voltage and resistance.
Look at the water spraying out of this garden hose. You have to be careful using water around power tools and
electric outlets because water can conduct an electric current. But in some ways, water flowing through a hose is
like electric current flowing through a wire.
Introducing Ohm’s Law
For electric current to flow through a wire, there must be a source of voltage. Voltage is a difference in electric
potential energy. As you might have guessed, greater voltage results in more current. As electric current flows
through matter, particles of matter resist the moving charges. This is called resistance, and greater resistance results
in less current. These relationships between electric current, voltage, and resistance were first demonstrated in the
early 1800s by a German scientist named Georg Ohm, so they are referred to as Ohm’s law. Ohm’s lawcan be
represented by the following equation.
Current(amps) =ResistanceVoltage(volts(ohms))Understanding Ohm’s Law
Ohm’s law may be easier to understand with an analogy. Current flowing through a wire is like water flowing
through a hose. Increasing voltage with a higher-volt battery increases the current. This is like opening the tap wider
so more water flows through the hose. Increasing resistance reduces the current. This is like stepping on the hose so
less water can flow through it. If you still aren’t sure about the relationships among current, voltage, and resistance,
watch the video at this URL: http://www.youtube.com/watch?v=KvVTh3ak5dQ