1) Atoms are made up of positively charged protons, negatively charged electrons, and neutral neutrons. 2) A deficiency or excess of electrons gives a positive or negative charge, measured in coulombs. 3) Coulomb's law states that the electrostatic force between two charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.

1. From the study of the structure of
matter, we learned that it is made up of
atoms contain positively charged
protons, negatively charged electrons,
and neutral particles called neutrons.
Introduction to Electricity & Magnetism.

2. We found that a deficiency in electron is
said to be positively charged, while an excess
of the same is negatively charged. These
electrons are expressed in coulombs (C)
which was named after the French physicist
Charles Augustin de Coulomb.
A coulomb is equal to 6.25x1018
electrons.

3. In his experiment, he came up to the
conclusion that forces of attraction or
repulsion closely followed Newton’s Law
of Universal Gravitation and can be
summarized in what was called as
“Coulomb’s Law of Electrostatics”.

4. It states that “the force of attraction
or repulsion between two charged objects
is directly proportional to the product of
their charge magnitudes and is inversely
proportional to the square of the distance
between them”.

5. When electron flows from one object
to another called conductor, it is now
termed as current. Its source is called a
generator, which increases the potential
difference of the electrons passing
through the conducting system.

7. However, the current flowing through the wire
is affected by an increase in potential difference or
voltage and by the increase in resistance in the circuit.
This was investigated by a German physicist George
Simon Ohm and results were summarized in his law
which states that: “the current flowing through a
circuit is directly proportional to the potential
difference and is inversely proportional to the
resistance in the same circuit”.

8. The rate of flow of electricity, called
current is measured in amperes (A) by an
ammeter. The potential difference is expressed
in volts (V) and is directly measured by a
voltmeter. R, the resistance to the flow of
electrons, is given in ohms (Ω) and is measured
using an ohmmeter.

10. A greater electrical pressure will
increase the current flowing through a
conductor if the conductor is made up of
the same material, of the same length, of
the same diameter, and if the temperature
remains constant.

11. Those are the factors that affect the
flow of current in the conducting wire.
But the material, whatever it was made
up from, has always the capacity to resist
flow. This is termed as its resistivity,
which is expressed in ohms-meter (Ω.m).

12. On the other hand, the region around the
charged body is described as an electric field. It is
where an electric force acts on a charged body. The
strength of an electrostatic field or the pressure that
is normal to the region where there is an electric
force is called electric field intensity, Ie.
It may be found by dividing the electric force F
by the charge q.
Ie = F /q
where the unit is Newton per Coulomb, or N/C

13. Example Problem on Coulomb’s Law:
Two objects are both negatively
charged with 0.02 C each and are 70 cm
apart. What kind of force exist between them
and how much?
Given: q1 = q2 = -0.02 C
d = 70cm = 0.70m
k = 9 x 109 N.m2/C2
Find: F (force existing between the
objects)

15. Example Problem on Coulomb’s Law:
A charge of 1.5 uC present in an
electric field produces a force of 0.06N.
What is the intensity of the electric field?
Given: q = 1.5 uC
F = 0.06N
Find: electric field intensity, Ie

16. Solution :
Ie = F /q
Ie = F /q
Ie = 0.06 N ÷1.5 x 10-6 C
Ie = 4.0 x 104 N/C