Electric Charge
Electric charge is a property of some particles that causes them to experience a force in an electromagnetic field. It can be either positive or negative. For example, an electron has a negative electric charge and a proton has a positive electric charge.
Electric charge (Q) can be calculated using the following equation:
Where I is current measured in amperes (A) and t is the time measured in seconds (s).
From the equation we can see that the units of electric charge can be given as As. The SI unit of electric charge, however, is the Coulomb (C).
Coulomb – one coulomb is the amount of charge supplied by a current of one ampere in one second.
Current
Current – The rate of flow of electric charge.
Essentially we get a current when particles with an electric charge move from one place to another. For example, in a wire electrons (negatively charged particles) flow through the metal in the wire (usually copper) to produce a current.
The equation for electric charge can be rearranged for current to give:
As mentioned above the SI unit for current is the ampere:
Ampere – one ampere is the amount of electric current equal to one coulomb per second.
Worked Examples
Example 1
Calculate the time taken for a charge of 1500C to pass through a wire when the current is 17A.
Example 2
Calculate the amount of electrons that pass through a point on a wire that has a current of 0.3A in 7 minutes. The charge of one electron is 1.6×10-19 C.
Example 3
14×1020 electrons pass through the point of a wire in 1200s. Calculate the current flowing through the wire. The charge of one electron is 1.6×10-19 C.
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