ElectrostaticsElectrostatics is the study of electric

charge at rest. (Or more or less at rest, in contrast with

current electricity.)

Electrical ChargesElectric charge is a fundamental

property of matter. Two types of electric charges

Positive charge - every proton has a single positive charge.

Negative charge - every electron has a single negative charge.

Proton and Electron

Protons• Positively-charged• Charge: q = +e = +1.602 x 10-19 Coulombs (C)• Mass: 1.673 x 10-27 kg

Electron• Negatively-charged• Charge: q = -e = -1.602 x 10-19 Coulombs (C)• Mass: 9.11 x 10-31 kg

Charged and Neutral ObjectsAn object with an excess of electrons

is negatively charged.An object with too few electrons (too

many protons) is positively charged.An object with the same number of

electrons and protons is neutral.

Charge is conservedElectric charge is conserved – it cannot

be created or destroyed. It can only move from one object to another.

Charge is quantized• The smallest value of charge an object can have is e = 1.602 x 10-19 C.

• The rest of the values are whole number multiples of e.

Example: 3e, 500e, 1.2 x 107 e

• You can never find an object that has a charge that is a fraction of e. This that an object cannot have a charge of (4/5)e, 2.25e, 15.09e.

Charging by Friction If one neutral material has more affinity

for electrons than another (neutral) material, it will attract electrons from the other.

One material becomes negatively charged, the other positively charged.

Charging by Contact If a charged object is brought in contact

with a neutral object, charges will be repelled from (or attracted to) the charged object.

The neutral object will gain a charge of the same sign as the charged object.

This is also called charging by conduction.

Polarization Bringing a charged object near (but not

touching) a neutral object polarizes (temporarily separates) the charge of the neutral object. Like charges in the neutral object are

repelled by the charged object. Unlike charges in the neutral object are

attracted by the neutral object. The neutral object returns to normal when the

charged object is removed. This is also called charging by induction.

COULOMB’S LAW- law of physics describing the electrostatic

interaction between electrically charged particles.

Coulomb’s law

The magnitude of the electrostatic force of interaction between two point charges is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance between them.

Coulomb’s law equation

F = force in Newtons (N)

q1 and q2 = charges in Coulomb (C)

r = distance between q1 and q2 in meters (m)

k = Coulomb constant

= 9.0 x 109

Note: Do not include the signs of the charges when using this equation.

Remember: If the signs of the charges are the same, the force is repulsive. If the signs are different (i.e., one positive and one negative), the force is attractive.

Electrical Forces

Like charges repel.Opposite charges attract.