(EAM) Ohm's Law Lesson

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 law can be represented by the following mathematical equation.

Current (amps) = $\frac{\text{voltage (volts)}}{\text{resistance (ohms)}}$

Before we look further at Ohm's law, it is important to know each term. At the start of this lesson, we discussed electrical current. It is important to remember that an electric current is a continuous flow of electric charges (electrons). Current is measured as the amount of charge that flows past a given point in a certain amount of time. The SI unit for electric current is the ampere ( A ), or amp. Electric current may flow in just one direction (direct current), or it may keep reversing direction (alternating current).

Electric potential energy comes from the position of a charged particle in an electric field. For example, when two negative charges are close together, they have potential energy because they repel each other and have the potential to push apart. If the charges actually move apart, their potential energy decreases. 

For an electric charge to move from one position to another, there must be a difference in electric potential energy between the two positions. A difference in electric potential energy is called voltage. The SI unit for voltage is the volt ( V ). For example, think about a circuit with a 1.5-volt battery. The difference of 1.5 volts between the two battery terminals results in a spontaneous flow of charges, or electric current, between them. The current then flows from the negative terminal to the positive terminal, because electric current is a flow of negatively charged electrons. If there is no potential difference then there is nothing to cause the electrons to flow.    

Lastly, resistance is opposition to the flow of electric charges in an electric current as it travels through matter. The SI unit for resistance is the ohm ($\Omega$).

Now that you know what each of the terms mean, let's jump into 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. Watch the following video for a further explanation and demonstration of the relationship between voltage, current, and resistance. 

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