Electric current

Charge & Current - OCR A-Level Physics

Key Definition

Electric current
The rate of flow of charge. Measured in amperes (A).

I = \frac{\Delta Q}{\Delta t}

Key Definition

One ampere
A current of 1 A means 1 coulomb of charge flows per second.

The ampereThe SI unit of current. One ampere is a flow of one coulomb of charge per second. (A) is an SI base unit.
Rearranged: $Q = It gives$ total chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). from 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). and time.
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 measured with an ammeterAn instrument that measures currentThe rate of flow of charge. Measured in amperes (A).. Connected in series with the component. Has very low resistanceThe opposition to current flow. The ratio of potential difference to current. Measured in ohms (Ω). so it doesn't affect the circuit. connected in series.
An ideal ammeterAn instrument that measures current. Connected in series with the component. Has very low resistance so it doesn't affect the circuit. has zero resistanceThe opposition to current flow. The ratio of potential difference to current. Measured in ohms (Ω). so it does not affect the current.

Examiner Tips and Tricks

Learn these basic recall facts from the specification.
They are easy marks that students often throw away by not memorising exact definitions.

Common Mistake MEDIUM

Wrong: Forgetting to convert time to seconds in $Q = It calculations$.
Right: Always convert: 1 minute = 60 s, 1 $hour = 3600 s. A common exam trap$ is giving time in minutes.