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ELECTROSTATICS
ELECTROSTATIC FORCE
What causes an electron to "orbit" the nucleus of
an atom?
 Electrons orbit the nucleus because of attractive
forces between the protons in the nucleus and
electrons in the orbital shells.
 This force is called the electrostatic force

COULOMB’S LAW


Charles Coulomb stated that the force
exerted between two charged particles
is directly proportional to the
magnitude of the two charges and
inversely proportional to the square of
the distance between them.
Sound familiar??
COULOMB’S LAW
𝑘𝐸 𝑞1 𝑞2
𝐹𝐸 =
𝑟2
𝐹𝐸 = Electrostatic Force
 𝑘𝐸 = Coulomb’s constant (8.99 x 109)
 𝑞1 = charge on object 1 (unit: Coulombs)
 𝑞2 = charge on object 2
 𝑟 = distance between objects

ELECTROSTATIC INTERACTION
Because of this electrostatic force, charged
particles will either attract or repel each other
depending on their charge.
 If the two charges are "like" charges, such as a
proton and a proton or an electron and an
electron, the "like" charges will result in a
repulsive force.

ELECTROSTATIC INTERACTION

If the charges are "unlike", such as a positive
charge and a negative charge, the "unlike"
charges will result in an attractive force.
IN AN EQUATION

When performing calculations for the electric
force, a positive answer indicates a repulsive
force and a negative answer indicates an
attractive force.
ELECTRIC FIELD
A free charged particle causes an electric field to
be around the charge.
 For a positive charge, electric field lines start at
the charge and point outward.

ELECTRIC FIELD
For a negative charge, the electric field lines
come from out in space towards the center of the
charge.
 The electric field depicts the direction of the force
the charged particle would exert on another.

ELECTRIC FIELD LINES

Field lines can be drawn between different kinds
of charges to analyze the force they would exert
on each other.
Attractive Force
Repulsive Force
ELECTRIC FIELD STRENGTH
The electric field created by a point
charge(negative or positive) is directly
proportional to the amount of charge the object
has and inversely proportional to the distance
between the two objects.
 In both situations, whether the object creating
the field is positive or negative, the charged
object placed at the distance r is assumed to be
positive.

ELECTRIC FIELD STRENGTH
E=
𝑘𝐸 𝑄
𝑟
E = Electric Field
 𝑘𝐸 = Coulomb’s constant (8.99 x 109)
 𝑄 = charge on the object
 𝑟 = distance from object

EXAMPLE PROBLEM 1

Calculate the electric field between a proton and an
electron in a hydrogen atom. The charge on a single
proton is 1.602 x10-19 C and the electron orbits the
hydrogen nucleus at a radius of 1.008 x10-10 m.
Draw a diagram of the electric field between the
proton and the electron
EXAMPLE PROBLEM 2

The charge on an electron is -1.602 x10-19 C. Find
the electric force exerted by the proton on the
electron in a hydrogen atom.