1. **Ohm's Law** deals
with the relationship between voltage and current in an ideal conductor. This
relationship states that:

**The potential difference (voltage) across an ideal conductor is
proportional to the current through it.**

The constant of proportionality is called the "resistance", **R**.

Ohm's Law is given by:

3. Ohm's Law can be used to solve simple circuits. A complete circuit is one which is a closed loop. It contains at least one source of voltage (thus providing an increase of potential energy), and at least one potential drop i.e., a place where potential energy decreases. The sum of the voltages around a complete circuit is zero.

4. An increase of potential energy in a circuit causes a charge to move from a lower to a higher potential (ie. voltage). Note the difference between potential energy and potential.

Because of the electrostatic force, which tries to move a positive charge
from a higher to a lower potential, there must be another 'force' to move charge
from a lower potential to a higher inside the battery. This so-called force is
called the **electromotive force**, or **emf**. The SI unit for the emf is
a volt (and thus this is not really a force, despite its name). We will use a
script E, the symbol ,
to represent the emf.

A decrease of potential energy can occur by various means. For example, heat lost in a circuit due to some electrical resistance could be one source of energy drop.

Because energy is conserved,
the potential difference across an emf must be equal to the potential difference
across the rest of the circuit. That is, Ohm's Law will be satisfied:

Press here

Example Problem on Ohm's Law

Continue to: Resistors in Series

Self Test

Return to: D.C. Circuits Menu

Return to: Physics Tutorial Menu