Ohm's law states that the current through a metallic conductor is directly proportional to the potential difference across it, provided that its temperature and other physical conditions stay constant.The resistance of a component is defined as R = V/I, measured in ohms (Ω), where 1 Ω = 1 V A-1. This definition applies to every component, whether or not it obeys Ohm's law.A component that obeys Ohm's law is called an ohmic conductor. Its current-potential difference graph is a straight line through the origin, and its resistance is constant.Components such as filament lamps, diodes and thermistors do not obey Ohm's law, because their resistance changes as the current or temperature changes. They are non-ohmic.Resistance can be combined with the power equations. Since P = IV and V = IR, the power is also P = I2R = V2/R. A 1.0 kW heater running at 230 V has a resistance of 2302 ÷ 1000 = 52.9 Ω.
Ohm's Law
Read the text
Read the text and highlight anything you think is important. When you go on, the text is hidden and you answer from memory.
Specification: AQA Physics (7407), AS-level, 3.5.1.2 Current-voltage characteristics. Topic: Electric Current.
Key terms in this lesson
- Electromotive force
- The electrical energy produced per unit charge by a source, such as a cell, in driving current around a circuit.
- Potential difference
- The energy transferred per unit charge as charge moves between two points in a circuit.
- Resistance
- The ratio of the potential difference across a component to the current flowing through it, measured in ohms.
- Internal resistance
- The resistance within a source of e.m.f., such as a cell, which causes a loss of potential difference, or lost volts, when current flows through it.
More in Electric Current
- Energy Transfer
- Electric Power
- Resistance
- Measuring Resistance
- Resistivity
- Superconductivity
- Electronic Components
- Investigating the Characteristics of Components
All 20 lessons in Electric Current · All AQA AS-level Physics topics