Physics

3.3 - Charge, Current & Time

6 min

What charge is

The Q = It equation

Finding the current

note 1 of 3

Current is a flow of charge

An electric current is a flow of electric charge, and is the rate of flow of charge.
In metals, the moving charge is carried by free electrons.
Current is measured in amperes (A).

The circuit is complete (a closed loop), with no gaps.
There is a source of potential difference (p.d.), such as a cell or battery, to push the charge around.

note 2 of 3

Charge is measured in coulombs (C).
A current of 1 ampere flows when a charge of 1 coulomb passes a point each second.

$Q = I t$

note 3 of 3

A current of 1.5 A flows through a lamp for 2.0 hours. How much charge passes through the lamp?

$t = 2.0 \times 60 \times 60 = 7,200 s$

$Q = I t = 1.5 \times 7,200 = 10,800 C$

So 10,800 coulombs of charge pass through the lamp.

key terms

TermDefinition

CurrentThe rate of flow of electric charge.

end of notes

Current is a flow of charge

An electric current is a flow of electric charge, and is the rate of flow of charge.

In metals, the moving charge is carried by free electrons.

Current is measured in amperes (A).

Conditions for current to flow

The circuit is complete (a closed loop), with no gaps.

There is a source of potential difference (p.d.), such as a cell or battery, to push the charge around.