Physics Study Guide/Theories of Electricity
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.
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
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
All the lines of force between charges and the surrounding made up an Electric Field E directly proportional to force
The force between 2 stationary charges is called Coulomb's 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
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
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.
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
- = ρ
Therefore, the conduction of all material can be calculated by
- ρ =
If there exists a straight line conductor. As shown above, every conductor has a Resistance R equal to the ratio of Voltage over Current
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
If there are n resistors connected in parallel, then the total resistance is