ELECTRICITY

Electricity The Greeks discovered certain objects such as rods of amber could be rubbed with cat's fur and attract light objects like feathers. The Greeks used “Electric Force” to describe mysterious forces of attraction and repulsion when amber was rubbed on a piece of cloth. They didn’t understand it nor could they explain it. We know little more about it today. Neg charged electrons, pos charged protons and neutrons are neutral.

Electricity Fundamentals Atoms are neutrally charged The nucleus is composed of protons and neutrons. Neutrons have no charge Protons are positively charged Electrons in the orbitals are negatively charged

Electricity Some electrons, particularly in metals are loosely bound and can detach and become “free electrons” Free electrons as the name implies can move freely from atom to atom When a force or pressure is applied free electrons begin to move

Electricity The materials that allow the free movement of electrons are called CONDUCTORS The following metals are considered as the best conductors: Gold Silver Copper Aluminum

Electricity Non Conductors or Insulators: Dry Wood Glass Rubber Mica Asbestos Semi-Conductors: Silicon Semi-Conductors act a conductors in some circumstances and as insulators in others

Electricity For Charged Bodies Unlike charges attract Like charges repel Based on what was just stated you might wonder why electrons don’t collapse in on the nucleus. They don’t because the centrifugal force associated with their orbit cancels out their attraction to the nucleus. Demonstration of the wad of paper page 15

When you rub a rubber rod with fur electrons are transferred from the fur to the rod. The rod becomes negatively charged and the fur becomes positively charged.

The Triboelectric Sequence Asbestos . Fur (Rabbit) Glass Mica Wool Quartz Fur (Cat) Lead Silk Human Skin Aluminum Cotton Wood Amber Copper, Brass Rubber Sulfur Celluloid On contact between any two substances shown in the column, the one appearing above becomes positively charged and the one below becomes negatively charged.

Insulators & Conductors Insulator is a substance that does not allow the electrons to freely move. Conductor is a substance that does allow the electrons to freely move

Charged Conductors No matter what the shape of the conductor, excess charge always resides on its outer surface.

There is no charge on the inside wall of a hollow electrified conductor. Charge tends to concentrate on the pointed regions of a conductor.

METHODS OF CHARGING a. By Conduction

b. By Induction grounding

Electricity Electrical energy is transferred through conductors by means of movement of free electrons A material’s ability to conduct current flow determines whether it is a good or bad conductor Actually current flow moves quite slowly, more slowly than the minute hands on a clock

Electricity The force that moves electrons in a conductor can be called Voltage Electromotive Force Potential Difference

Static Electricity When an atom loses or gains electrons, it becomes positively or negatively charged, respectively. When a material becomes charged it will keep its positive or negative charge as long as it stays isolated from other materials (Static Charge) Once it comes in contact with another material the negative charge will flow to the positive. Should positively charged atoms come into contact with negatively charged atoms the negative charge will jump to the positive. The rubber sole example Electrons are much lighter than protons and protons are more or less attached to the nucleus so that is why electrons move to positive rather than the other way around

Coulomb's Law An electric force has the following properties: 1. It is inversely proportional to the square of the separation r between the two particles and is along the line joining them. 2. It is proportional to the product of the magnitudes of the charges and on the two particles. 3. It is attractive if the charges are of opposite sign and repulsive if the charges have the same sign.

Find the electric force between two 1. 00 C charges separated by 1 Find the electric force between two 1.00 C charges separated by 1.00 m.                                                                                                                                                                                                  

CIRCUITS In any electric circuit where electrons move around, three things are present: Voltage Current Resistance

VOLTAGE ( V or E) Six Methods of Producing Voltage Friction – Static electricity Pressure – Compression of crystals Heating – In copper electrons move away from the heat. In iron they move to the heat. Light – Photoelectric cells Chemical Action - Batteries Magnetism Pressure – crystals are squeezed to produce voltage Heating – Voltage can be produced by heating the joint where two unlike metals come in contact Light – Voltage is produced when light strike photosensitive substances Magnetism – voltage is produced in a conductor when it is moved through a magnetic field

CURRENT (I) Charges are measured in terms of Coulombs (C) One electron has a charge of 1.602 x 10 -19 C 1 Coulomb = 6.28 x 1018 electrons 6,280,000,000,000,000,000 electrons Ampere = 1 coulomb of charge flowing per second = basic unit of current = A

RESISTANCE (R) Measure of the opposition of the material to the flow of electrons. Insulators have high resistance; conductors have low resistance. Measured in terms of ohms (Ώ)

OHM’S LAW Ohms Law – The current in a circuit is directly proportional to the applied voltage and indirectly proportional to the circuits resistance. I = current measured in amperes (amps) E = Voltage R = Resistance in Ohms

OHM’S LAW APPLICATION Battery = 3 volts Resistance = 1.5 ohms Amperes = ? Amperes = 2

OHM’S LAW TRIANGLE Another way of writing ohms law:

ELECTRIC POWER - WATTS Watts is the name given to electrical flow – but what flows? Energy Energy is measures in joules A joule of electrical energy can move from place to place along the wires. The amount of energy that flows in one second is one watt.

ELECTRIC POWER - WATTS Power pertains to the rate at which work is being done. Work is done whenever a force causes motion i.e. when voltage causes electrons to move in a circuit work is done The rate at which this work is done is called the electric power rate and is measured in WATTS

ELECTRIC POWER - WATTS Watts = the amount of voltage across a circuit x the current through the circuit or Watts = Amperes x Volts P= I E

ELECTRIC POWER - WATTS P = Power in watts I = current in Amperes R = resistance in ohms