The Quantity of Charge, Q

Calculating the Quatity of Charge on an Object

The electron is the particle that accounts for the charge on an object.   Movement of electrons form and to the object will establish the type of charge the object will have.  The object will be positively charged where their is a  loss of electrons, negatively charged where there is a gain or surplus of electrons and neutral where the positive and negative charges are equal.

The total amount of electrons deposited or removed from the object will determine the quantity (the amount) of charge on the object.

The charge on one single electron is therefore defined as  the fundamental unit of charge.   Charge is a fundamental measurement which cannot be derived from any other measurements.  Charge is measured in units of Coulombs

The symbol for charge is "Q", and the symbol for Coulomb is "C".

The amount of charge on one single electron can be mathematically determined to equal a very small amount of charge.

This small charge is 1.6 X 10-19 C  this small amount of charge is known as the fundamental charge and its symbol is e (to remind us that it is the charge on one single electron).  This is a constant value.

Therefore  e = 1.6 X 10-19 C/e     [Coulombs per electron]

To calculate the total charge on an object we multiply the constant value of e by the number of electrons deposited  on (or removed from) an object.

A simple formula is used to summarize this important fact:

Q = N x e

Where:
is the total charge on an object, N is the number of electrons involved, and e is the fundamental; charge on one single electron (1.6 X 10-19 C/e)

Example:
If you walk across a carpet with your socks on and then touch a metal door knob you will feel a shock.  The amount of charge transferred in the shock between your fingers and the door knob (to ground) is about 3.0 X 1020 C.  How many electrons where transferred from the carpet to ground through your finger during the shock?

Solution:

Given

e = 1.6 X 10-19 C/e  (the fundamental charge constant)

Q = 3.0 X 1020 C  (total charge transferred)

Find:  N  (total number of electrons involved)

Q = N x e  N = Q/e

N = [3.0 X 1020 C]/[1.6 X 10-19 C/e]

N = 1.90 X 1039 electrons

Therefore 1.90 X 1039 electrons where transferred from the carpet to the door knob during the "shock"