Ohm's Law

Ohm's Law

Voltage pushes charge through a component.

Resistance makes that flow harder.

For an ordinary fixed resistor:

**V = IR**

Ohm's Law

Ohm's law states that for an ohmic conductor at constant physical conditions, especially constant temperature, the current through it is directly proportional to the potential difference across it.

V ∝ I

Therefore:

**V = IR**

where:

V = potential difference in volts I = current in amperes R = resistance in ohms

Resistance

Resistance measures how strongly a component opposes electric current.

**R = VI**

Unit:

ohm (Ω)

Ohmic Conductor

For an ohmic conductor maintained at constant temperature, a graph of V against I is a straight line through the origin.

The ratio `VI` remains constant.

Non-ohmic Behaviour

Not every component obeys Ohm's law under all conditions.

Examples include filament lamps, diodes, and thermistors.

Worked Example

A resistor has **V = 12 V** and **I = 3 A**.

**R = VI**

**R = 123 = 4 Ω**

Ohm's Law — Advanced

Ohm's law describes linear current-voltage behaviour under fixed physical conditions.

Resistance is the proportionality constant between V and I for an ohmic component.

A changing resistance causes a nonlinear characteristic.