# Physics Study Guide/Theories of Electricity

## Intro

All matter's atom is made of Charged Particles Called Electrons, Neutron and Protons . Each Atom has a Nucleus at the center consists of Neutron and Proton and Electrons on circular orbits circulating around Nucleus.

## Charged Particle

There are three kinds of charged particles

1) Electron: particle that has a negative charge with a mass of x 10-30

2) Proton: particle that has a positive charge with a mass of x 10-27

3) Neutron: particle that has a zero charge with a mass of x 10-27

## Charge

Normally, all matter has a sum of Electric Charges equal to zero. When an object gives or receives Electrons will become Positively Charged or Negatively Charged.

Object + e -> -
Object - e -> +

A positively charged object has a quantity of charge +Q and Electric lines of force radiate outward.

A negatively charged object has a quantity of charge -Q and Electric lines of force radiate inward.

Like charges repel. Opposite charges attract. Negatively charged objects attract positively charged objects and vice versa.

## Force between two charges - Coulomb's Force

With one positive charge +Q and one negative charge -Q on a straight line at a distance r from each other, the negative charge will attract the positive charge with a force.

F = m a
a = k Q / r2
$F = k \frac{+Q -Q}{r^2}$

All the lines of force between charges and the surrounding made up an Electric Field E directly proportional to force

$E = \frac {F}{Q}$

The force between 2 stationary charges is called Coulomb's Force.

## Electrostatic Force

If there is a charge at rest. If there is a force that makes charge move then the force that makes the charge move is called Electromotive Force

FE = Q E

## Electromotive Force

When moving charge pass through a magnetic field that has direction from left to right. The magnetic field exerts a force on the charge to make it go up or down. Positive charge goes up, Negative charge goes down.

FB = Q V B

## Electromagnetic Force

For a moving charge the sum of Electrostatic Force and the Electromotive Force gives Electromagnetic Force acting on the charge

FEB = Q E + Q V B = Q (E + V B)

Electrostatic Force is the force generates Current going from left to right . Electromotive Force is the force generates Current going perpendicular to current of electrostatic

Electromagnetic Force generates an Electric Field going from left to right and a magnetic Field perpendicular to Electric Fiels

## Electricity and Conductors

In all conductors, charges move freely in any direction. If there is an Electric Force

FE = Q E

Electric Force will exert a pressure FE / A that force charges in conductor to move in a straight line. This action generates a current of charge moving in a straight line.

The Pressure from the Electric Force is called Voltage and the straight line of moving charges is called Current.

If Voltage is V and Current is I, then the ratio of Current over Voltage gives the Conductance of the Conductor and the ratio of Voltage over Current gives the Resistance of the conductor.

$G = \frac{I}{V}$
$Z = \frac{V}{I}$

Therefore, All conductors have a Resistance and a Conductance

If there exists a straight line conductor of length l, that has surface area A with conduction ρ then the Conductance of the conductor

G = ρ $\frac{l}{A}$

From above,

$G = \frac{I}{V}$ = ρ $\frac{l}{A}$

Therefore, the conduction of all material can be calculated by

ρ = $\frac{I}{V} \frac{A}{l}$

## Resistor

If there exists a straight line conductor. As shown above, every conductor has a Resistance R equal to the ratio of Voltage over Current

$R = \frac {V}{I}$
$I_R = \frac{V}{R}$

A straight line conductor has a capability of reducing current. This can be used in an electric circuit to reduce current. In an electric circuit, straight line conductor has a symbol --^^^-- with a resistance R measured in Ohms Ώ and is called a resistor.

Resistance can be connected in series or in parallel to increase Resistance or to decrease resistance.

If there are n resistors connected in a series, the total resistance is

$R_t = R_1 + R_2 + ... + R_n$

If there are n resistors connected in parallel, then the total resistance is

$\frac{1}{R_t} = \frac{1}{R_1} + \frac{1}{R_2} + ... + \frac{1}{R_n}$