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They’re Attractive & Repulsive at the Same Time
When two charges are brought together they either push away from each other or they pull
towards each other.
+ +
- -
Since the charges will change their motion, Newton’s First Law tells us they must have a force applied to them!!!!
Newton’s Third Law tells us that the force on each charge must be equal in size but opposite in direction. They are an action-reaction pair!!!!
If there is no net force acting on an object, then
Electric Charge
We know that there are two types of charge – positive and negative.
We know that protons are 2000 times bigger than electrons in terms of mass.
We know that even though protons are positively charged & electrons are negatively charged, protons and electrons carry the same size charge.
The size of the charge on a proton & an electron is defined in units called a Coulomb (C).
A Coulomb (C) is the unit used to measure electric charge.
Electric Charge
A Coulomb of charge is very large.
It would take 6.25 X 1018 protons to make 1-C of charge.
For those of you who avoid scientific notation like the plague: It takes 6,250,000,000,000,000,000 protons to make 1-C of charge.
A proton has a charge of 1.6 X 10-19-C, an electron has a charge of -1.6X 10-19-C.
For you anti-plague people:1.6 X 10-19-C = 0.000 000 000 000 000 000 16-C
Particle
Charge (C)
Mass (kg)
Proton 1.60 x 10-19 1.673 x 10-
27
Electron -1.60 x 10-19 9.109 x 10-
31
Neutron 01.675 x 10-
27
Coulomb’s LawIn 1875, Charles Coulomb did some experiments on the forces between electric charges.
He discovered two things:
1) The size of the force depends directly with the product of each charge..
FE ~ Q1∙Q2
Where Q is the size of the charge in Coulombs.
2) The size of the force depends inversely with the square of the distance between the charges.
FE ~ 1/r2
Where r is the distance between the charges.
Example
Find the electrical force between a 1-C charge and a 3-C charge that are 6-m apart.
Know Formula
Work
Q1 = 1-CQ2 = 3-Cr = 6-m
The (+) answer
means the force is
repulsive – LIKE
CHARGES REPEL
Example 2
Find the electrical force between a 5-C charge and a -5-C charge that are 100-m apart.
Know Formula
Work
Q1 = 5-CQ2 = -5-Cr = 100-m
The (-) answer
means the force is
attractive – opposite CHARGES
attract