The ampere is the SI unit of electric current. One ampere is the rate of flow of electric charge (electric current) when one coulomb of electric charge carriers passes through a certain point in an electric circuit on one second. The symbol for electric current is I and that for ampere is A.
Thus I= Q/t; where t is in seconds
Example
How long will it take 200 milli-coulombs of electric charge to pass through a fuse in an electric circuit if the current is 73 amperes?
Solution
I=Q/t
Therefore, t=Q/I
t=200×10ˉ/73
t=2.74×10ˉs
t=2.74ms
Volt
Electric potential difference (p.d.) between any two points in an electric circuit is defined as the rise (or fall) in potential energy involved in moving a unit quantity of electric charge from one point to the other. The volt is the SI unit of potential difference. From the definition of potential difference, one volt is the potential difference between two points in an electric circuit when the energy involved in moving one coulomb of electric charge from one point to another is one joule.
In an equation form, E (or V) = W/Q
Where E (or V) is the potential difference in volt, W is energy in Joule and Q is quantity of electric charge in Coulomb.
The Symbol for source voltage or applied voltage is E and that for voltage drop is V.
Resistance
Resistance is defined as the opposition of the flow of electric current in an electric circuit. The symbol for resistance is R. The Ohm is the SI unit for the measurement of electric resistance and it is represented with a symbol Ω.
