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Circuits, charge and current
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Electric current is a flow of charge. Circuit symbols and the charge equation are the starting point for every electricity question.
Circuit symbols
Current and charge
Current is the rate of flow of charge. In metals the charge is carried by electrons.
charge (C) = current (A) × time (s), or Q = I × t.
Current is measured in amperes (A); charge in coulombs (C).
charge (C) = current (A) × time (s), or Q = I × t.
Current is measured in amperes (A); charge in coulombs (C).
Potential difference
Potential difference is the energy transferred per unit charge: E = Q × V.
It is measured in volts (V). 1 volt = 1 joule per coulomb.
It is measured in volts (V). 1 volt = 1 joule per coulomb.
A current of 0.5 A flows for 2 minutes. How much charge flows?
- Change time to seconds: 2 × 60 = 120 s
- Q = I × t = 0.5 × 120
Answer: 60 C
Q = I × t. E = Q × V. Ammeters go in series, voltmeters in parallel. Current in metals is a flow of electrons.
The interactive lesson includes the diagrams for this topic.
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