ELECTRICITY AND MAGNETISM
Static, Currents, Circuits, Magnetic Fields & Electro Magnets, and Motors &
Generators
1. EARLY THEORIES ON CHARGES
In trying to explain electric charges, different theories come up. These are the
one fluid theory, the two fluid theory, and the dielectric theory.
ONE FLUID THEORY
 proposed by Benjamin Franklin.
 all bodies posses a certain amount of “electric fluid” needed to keep
them uncharged.
 when two bodies are rubbed together, one of the bodies get some of the
fluid from the other body. The body that loses some of the fluid become
negatively charged, one of the bodies get some this fluid becomes
positively charged.
TWO FLUID THEORY
 proposed by Charles Du Fay.
 all bodies contain equal amount of two kinds of fluid.
 when two bodies are rubbed together, one of these fluids spread over
one body making it positively charged while the other kind of fluid spreads
over the other body, making it negatively charged.
DIELECTRIC THEORY
 proposed by James Clerk Maxwell and Michael Faraday.
 considers charges as a form of strain in the hypothetical ether surrounding
a body.
 To charge a body is to strain the ether and to discharge it is to remove
strain.
ATOMS
 Have neutrons, protons, and electrons.
 Protons are positively charged
 Electrons are negatively charged
ELECTRONS
 Are located on the outer edges of atoms…they can be moved.
 A concentration of electrons in an atom creates a net negative charge.
 If electrons are stripped away, the atom becomes positively charged.
The world is filled with electrical charge
What is this electrical potential called?
STATIC ELECTRICITY
 The buildup of an electric charge on the surface of an object.
 The charge builds up but does not flow.
 Static electricity is potential energy. It does not move. It is stored.
STATIC DISCHARGE
Occurs when there is a loss of static electricity due to three possible things:
 Friction - rubbing
 Conduction – direct contact
 Induction – through an electrical field (not direct contact)
ELECTRICITY THAT MOVES
 Current: The flow of electrons from one place to another.
 Measured in amperes (amps)
 Kinetic energy
HOW CAN WE CONTROL CURRENTS?
 With circuits.
 Circuit: is a path for the flow of electrons. We use wires.
THERE ARE 2 TYPES OF CURRENTS:
 Direct Current (DC) – Where electrons flow in the same direction in a wire.
 Alternating Current (AC) – electrons flow in different directions in a wire
THERE ARE 2 TYPES OF CIRCUITS:
 Series Circuit: the components are lined up along one path. If the circuit is
broken, all components turn off.
 Parallel Circuit – there are several branching paths to the components. If the
circuit is broken at any one branch, only the components on that branch will turn
off.
CONDUCTORS VS. INSULATORS
 Conductors – material through which electric current flows easily.
 Insulators – materials through which electric current cannot move.
Examples
CONDUCTORS:
INSULATORS:
Metal
Water
Styrofoam
Rubber
Plastic
Paper
WHAT IS RESISTANCE?




The opposition to the flow of an electric current, producing heat.
The greater the resistance, the less current gets through.
Good conductors have low resistance.
Measured in ohms.
WHAT INFLUENCES RESISTANCE?




Material of wire – aluminum and copper have low resistance
Thickness – the thicker the wire the lower the resistance
Length – shorter wire has lower resistance
Temperature – lower temperature has lower resistance
WHAT IS VOLTAGE?
 The measure of energy given to the charge flowing in a circuit.
 The greater the voltage, the greater the force or “pressure” that drives the
charge through the circuit.
DIFFERENCE BETWEEN VOLTS AND AMPS
Example – you could say that…
 Amps measure how much water comes out of a hose.
 Volts measure how hard the water comes out of a hose.
OHM’S LAW
 Resistance = Voltage / Current
 Ohms = Volts / Amps
WHAT IS AN ELECTROMAGNET?
 Electromagnet – a magnet made from a current bearing coil of wire wrapped
around an iron or steel core.
WHAT IS A GENERATOR?
 Generator – a machine that changes mechanical energy to electrical energy
 Usually use moving magnets to create currents in coils of wire.
WHAT IS A MOTOR?
 Motor – a device that changes electrical energy to mechanical energy that can
do work.
Watts = Amps x Volts
Amps = Watts / Volts
Volts = Watts / Amps