Ohm's Law — Definition

Definition

Imagine you have a pipe through which water flows. The amount of water flowing per second is like electric current, and the 'push' or pressure difference making the water flow is like voltage. The narrowness or friction in the pipe that resists the water flow is analogous to electrical resistance. Ohm's Law simply tells us how these three things are related in an electrical circuit.

In simpler terms, Ohm's Law states that if you apply a certain 'push' (voltage) across a material, a certain amount of 'flow' (current) will pass through it. The 'resistance' of the material determines how much current flows for a given voltage. If the resistance is high, less current will flow for the same voltage. If the resistance is low, more current will flow.

Specifically, the law says that the current ($I$) is directly proportional to the voltage ($V$) applied across the ends of a conductor. This means if you double the voltage, you double the current, assuming the conductor's properties don't change. This proportionality is maintained by a constant factor, which we call resistance ($R$). So, the mathematical relationship becomes $V = IR$.

Here's what each term means:

Voltage (V) — Also known as potential difference, it's the 'electrical pressure' or the energy per unit charge that drives the current. Measured in Volts (V).
Current (I) — The rate of flow of electric charge. It's how many electrons pass a point in the circuit per second. Measured in Amperes (A).
Resistance (R) — The opposition offered by the material to the flow of electric current. It's a measure of how difficult it is for electrons to move through the material. Measured in Ohms ($Omega$).

It's crucial to remember that Ohm's Law applies only under certain conditions, primarily that the temperature of the conductor remains constant. Many materials, especially semiconductors, do not strictly obey Ohm's Law, and are thus called 'non-Ohmic' conductors. However, for most metallic conductors at constant temperature, it provides a very accurate and useful model for circuit analysis.