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 T3.  CALCULATING QUANTITY OF ELECTRIC CHARGE 

Relationship between electric charge, Q and electric current, I

In electrolytic processes, the extent of reaction is governed by a number of factors, usually the most important being the amount of electricity passed:

electric charge /C  =  electric current /A  x  time /s

In SI quantity symbols

Q  =  I  x  t

The coulomb is defined from this relationship between the physical quantities.

One coulomb of charge passes a point in a circuit when a current of one amp flows for one second.

Example

Calculate the quantity of charge passing in an electrical circuit when a current of 5.0 A flows for 130 s.

Realtionship
between
physical quantities

Q  =  I  x  t

I = 5.0 A

t = 130 s

Q  =  ? to find

needs no re-arrangement
so quantities can be substituted in directly

Q  =  5.0 A  x  130 s

Q  =  650 A s

..

.

or  Q  =  650 C

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