GEN PHYS 2 | Electric Charge & Coulumb's Law

Charges’ Behavior

• There are two charges: one positive and negative.

• Similar charges repel while opposite ones attract.

Ionization

• causes charges to occur

• when total number of protons equal the ones of the electrons, the total charge is zero

• excess negative charge is obtained through changing the number of positive charge through transferring electrons, protons do not move as they are in the nucleus.

• a positively charged atom is the complement of a negatively charged one

Proton

• positive charge

• has a mass of 1.673 × 10^-27

Neutron

• zero charge

• has a mass of 1.675 × 10^-27

Electron

• negative charge

• has a mass of 9.109 × 10^-31

Conservation of Charge

• algebraic sum of all charges in a closed system is constant

• charge is neither destroyed nor created, merely transferred

• no experimental evidence has violated this

Quantization of Charge

• magnitude of an electric charge is an integer multiple of e = 1.6 × 10^-19

• known as elementary charge

Conductors

permit electric charges to move easily from one region of material to another

Insulator

prevent charges from leaving material

Semiconductors

intermediate to properties between conductors and insulators

Ways to Charge Objects

• rubbing/friction

• conduction/contact

• induction

Charging by Friction

When two different materials are rubbed together, electrons are transferred from one material to another. The object that loses electrons becomes positively charged, while the one that gains electrons becomes negatively charged.

Charging by Conduction

A charged object touches a neutral conductor, transferring electrons by direct contact. Both objects end up with the same type of charge.

Charging by Induction

A method of charging an object without direct contact. A charged object brought near a conductor causes charges in the conductor to rearrange, leading to induced charges.

When a charged object is far away from an uncharged one, what happens?

They attract each other.

When a charged object is touching an uncharged one, what happens?

They repel.

Polarization

occurs when charged objects cause slight shifting if charges within the molecules of a neutral object

Coulumb’s Law

Charles Augustin de Coulumb studied the interaction of charged particles i 1784. This law states that the magnitude of the force applied by an electric charge is

• directly proportional to the product of the charges

• inversly proportional to the square of the distance between them

Value of Coulumb’s Constant

k = 9.00 × 10⁹

Number of electrons in 1 Coulumb

1 C = 6.25 × 10¹⁸

Superposition Principle

Net electric force is the vector sum of all forces acting on the charge.