Electric
Force

**Coulomb's law**, developed in the 1780s by French physicist Charles Augustin de Coulomb, may be stated as follows:

*The ***magnitude** of the electrostatic force between two point electric charges is directly proportional to the product of the magnitudes of each charge and inversely proportional to the square of the distance between the charges.

*The ***direction** of that force is directed towards a point between them if they are of opposite charge to each other and away from it if they are both of the same type of charge.

The **Coulomb Fo****rce** is the electric force (that acts on charges) is given by the following
equation:

where _{o}
is the permitivitty of free
space,

Q_{1} and Q_{2} are the charges and

r is the
distance they are apart

The Coulomb force is a force - so it is a vector!

(a positive
result indicates a repulsive force (two negative charges or two positives
will result in that), whereas a negative result indicates an attractive
result (one charge of each type will result in that))

The **gravitational force
**(that acts on masses) is given my the following equation:

(the negative sign shows that the force is always attractive)

where G is
the gravitational constant, m_{1} and m_{2} are the
masses and r is the distance they are apart.
Can you see the similarity? The examiners will expect you to!

Consider two electrons one
metre apart:

- mass of
the electron m
_{e} = 9.11 x 10^{-31} kg
- charge on the electron Q
_{e} = 1.60 x 10^{-19} C
- G = 6.67 x 10
^{-11} m^{3} kg^{-1} s^{-2}
_{o}
= 8.85 x 10^{-12} F m^{-1}

The **gravitational force** acting
on the two electrons is 8.3 X 10 ^{-61} N

The **coulomb force acting** on the two electrons is 2.3 x 10^{-28 }N

Therefore the coulomb force
is 10^{32} times bigger than the gravitational force (100,000,000,000,000,000,000,000,000,000,000
times bigger).... that's why we have to think of charges as being in
a different dimension to us.... they experience the 'hills and dales of the electric
field' much more strongly than the 'ups and downs' of the gravitational field.

**LOJ MARCH
2002**