OCR.4.1.2
resistance
Energy, Power & Resistance - OCR A-Level Physics
Key Definition
resistance
A measure of the difficulty of making current pass through a component. Defined by R = V/I.
A measure of the difficulty of making current pass through a component. Defined by R = V/I.
$$R = \frac{V}{I}$$
Key Definition
Ohm's law
The current through a metallic conductor is directly proportional to the potential difference across it, provided physical conditions (e.g. temperature) do not change.
The current through a metallic conductor is directly proportional to the potential difference across it, provided physical conditions (e.g. temperature) do not change.
- A component obeying Ohm's lawFor an ohmic conductor at constant temperature, currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A). is directly proportional to potential difference. is called an ohmic conductorA conductor that obeys Ohm's law: currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A). is directly proportional to potential differenceThe energyThe capacity to do work. Measured in joules (J). transferred per unit chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). between two points. Measured in volts (V). at constant temperature..
- For an ohmic conductorA conductor that obeys Ohm's law: currentThe rate of flow of charge. Measured in amperes (A). is directly proportional to potential difference at constant temperature., R is constant at all values of V.
- The unit of resistanceThe opposition to current flow. The ratio of potential difference to current. Measured in ohms (Ω). is the ohmThe SI unit of resistance. 1 Ω = 1 V/A — the resistance when 1 V drives a current of 1 A. (ohm). 1 ohm = 1 $V A^{-1}$.
- $R =\;\text{V}/I is a definition. It applies to\;\text{A}LL components.$
- Ohm's lawFor an ohmic conductorA conductor that obeys Ohm's law: current is directly proportional to potential difference at constant temperature. at constant temperature, current is directly proportional to potential differenceThe energyThe capacity to do work. Measured in joules (J). transferred per unit charge between two points. Measured in volts (V).. is a special case: it only applies when R is constant.
Common Mistake
MEDIUM
Treating $R = V/I$ as Ohm's lawFor an ohmic conductor at constant temperature, current is directly proportional to potential difference.. $R = V/I$ is just the definition of resistanceThe opposition to current flow. The ratio of potential difference to current. Measured in ohms (Ω).. Ohm's lawFor an ohmic conductor at constant temperature, current is directly proportional to potential difference. states that V and I are proportional (constant R), which only holds for ohmic conductors.
Related:Current Electricity
Circuits Kirchhoff