PhysicsChapter 7: Current Electricity
Ohm's Law
Introduction
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
Definition
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**
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Ohm's Law
Sticky Notes · Quick Revision
OHM'S LAW
- V = IR
RESISTANCE
- Opposition to current
UNIT
- Ω
60-second revision
- **V = IR**
- **R = VI**
- Unit → ohm.
- Ohmic → straight-line V-I relation.
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