Electrostatics
1) Coulomb’s Law of Electrostatic Force
From experimentation with electrically charged objects, Coulomb was
able to determine the factors that affect electric force (FE):
Note:
From experiments similar to the Cavendish exp., the value of k was found:
Compare the electrostatic constant to the universal gravitational
constant:
This shows the relative strength of electric force compared to
gravitational force.
The unit of electric charge is the Coulomb(C).
1C=
1 elementary charge =
What is the force between two 1 C charges spaced 1m apart?
Typically we use units like mC, μC or nC in electric force calculations.
When a combination of charges is present, we must use vector analysis
to determine the net force acting.
Eg1) Find the net force acting on q1 shown below:
q1= +8.0 μC
q2 = -7.0 μC
q3 = +9.0 μC
Eg2) Find the net force on q1
2.0 m
2.0 m
Eg3) Consider two 100 g masses with a positive charge hanging as shown.
Find the charge acting on each.
75 cm
15 cm