Protons and electrons each have qualities called positive electric charge and negative electric charge .
Like charges repel each other, and different charges attract each other.
Charges of Matters
A matter is said to be charged when there is an imbalance of protons and electrons.
The greater the accumulation of electrons is, the stronger the charge.
Charge is measured in coulombs (C).
An electron is -1.6*10 -19 C.
Charles Augustin de Coulomb
Born in 1736, died in 1806
Created a device that helped him develop his theories on charges and electric force and field.
Invented by Coulomb to measure very weak force
Contributed in the creation of Coulomb’s Law by measuring Coulomb’s Constant
Also used by Henry Cavendish to find the gravitational constant.
Coulomb’s sketch of his invention
How It Works
When an unknown force is applied to the metallic object or plates in the container, the object spins.
The greater the force is, the bigger the angle.
What is Coulomb’s Law
The magnitudes of the electrostatic force between two point electric charges are directly proportional to the product of the magnitudes of each charge and inversely proportional to the square of the distance between the charges.
The strongest formula in the universe
Coulomb's law is fully accurate only when the objects are stationary, and remains approximately correct only for slow movement. These conditions are collectively known as the electrostatic approximation .
Similarity to Gravitational Force
Electric force and gravitational force both measure magnitudes of certain forces between two bodies .
Therefore, they are both directly proportional to the magnitudes of two bodies and inversely proportional to the squares of distances .
K , Coulomb’s Constant
K = 9*10^9 N*m 2 /C 2
Being one of the constants with biggest numbers, Coulomb’s Constant shows that electromagnetic force is one of the strongest forces in the universe.
Vector of Coulomb’s Law
Electric force is a vector force.
The first vector value is the sign of force, since the force can be either negative or positive.
The second vector value is the angle and direction to which the force heads.
F 2 = F 1->2 + F 3->2
With direction and sign known, multiples of electric forces can be calculated into a net force.
The resulting force is F on 2, since q2 is repelled away by q3 and attracted to q1, because of charge movements.
Every charge has an electric field associated with it.
Electric field of a charge is an area in which the charge has electric force.
Rules in Drawing Field Lines
Electric field lines always go from positive to negative.
The stronger the electric field is, the more the field lines.
Dense field line web depicts strong electric field.
Field lines never cross each other.
Coulomb’s Law - Field
Based on his law, Coulomb was able to derive another formula.
Since this formula is for a single point charge, only the magnitude of that charge is needed.
E = Kq/d^2
Electric Field of Higher Dimensions
Since e. field of a point charge(0 th Dimension) is kq/r^2, those of line charge(2 nd ) and plane charge(3 rd ) will become kq/r and kq.
Leduc, Steven. Cracking The AP Physics EXAM .Princeton Review, 2005.
Gewirtz, Herman, Barron’s SAT Physics. Barron’s, 2007
Henderson, Tom. Electric Field Intensity. Physics Course Class Room. 1996-2007. <http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/estatics/u8l4b.html
Nave, Carl R. "Electric forces." Hyperphysics . Georgia State University. 30 May 2008 <http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html>.