Electricity & Magnetism

Electricity & Magnetism Static, Currents, Circuits Magnetic Fields & Electro Magnets Motors & Generators

Atoms… • Have neutrons, protons, and electrons. • Protons are positively charged • Electrons are negatively charged

An Atom

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.

Atoms with an excess of electrons are called negative ions and those that are missing electrons in the shells or orbits are called positive ions.

The world is filled with electrical charges: + - + + + - + - - + + + - - - + + - - -

THE LAW OF CONSERVATION OF CHARGE • THE LAW OF CONSERVATION OF CHARGE STATES THAT AN ELECTRIC CHARGE CANNOT BE CREATED OR DESTROYED.

Electricity • Electricity is the movement of free electrons in a material toward an area of positive (+) charges. • The conduction of those electrons is determined by the type of material.

A buildup of opposite charges creates an electric potential. • Release of the potential energy results in the movement of free electrons, which is called electricity.

Types of Electricity • Static electricity • Current electricity • Direct current • Alternating current

What is this electrical potential called? • Static Electricity - - - - - + + + - - + +

Static Electricity • The build up 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 • Nonconduction (Insulators) – 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.

There are 2 types of currents: • Alternating Current (AC) – electrons flow in different directions in a wire

Circuits • Electric Circuits • Devices rely on a source of electrical energy and wires to complete an electric circuits. • Circuits typically include: • A voltage source • A conductor (such as a wire) • A device that uses the electrical energy to do work.

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.

Series Circuit

There are 2 types of circuits: • 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.

Parallel Circuit

Conductors vs. Insulators • Conductors – material through which electric current flows easily. • Insulators – materials through which electric current cannot move.

Conductors • Solid metals are good conductors of electricity, because electrons are allowed to move freely throughout the material. • Copper and gold are some of the best conductors of electricity.

Insulators (Nonconductors) • Nonconductors inhibit the movement of electrons within the material. But they often do allow electrons and ions to collect on their surfaces. Examples of nonconductors or electrical insulators are: • Plastic • Rubber • Glass • Most metal oxides (like rust) • Air • Oil • Pure, de-ionized water

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

Electric Current can be measured with an instrument called an AMMETER. The AMMETER determines how much charge passes through it every Second. • THIS MOVEMENT, OR CURRENT, IS MEASURED IN SI UNITS CALLED AMPERES (A).

What is Voltage? • The measure of energy given to the charge flowing in a circuit. • The SI unit is volts with the symbol (V) • The greater the voltage, the greater the force or “pressure” that drives the charge through the circuit.

Difference b/t 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 V = I x R • Resistance = Voltage / Current • Ohms = Volts / Amps where I is the current in amperes, V is the potential difference between two points of interest in volts, and R is a constant, measured in ohms, called the resistance.

Practice with Ohm’s Law

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.

That’s It !!!!

Electricity & Magnetism