Electricity & Magnetism Static, Currents, & Electro Magnets Motors & Generators

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 charges: + - + + + - - + - + + + - - - + + - - -

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 Induction – through an electrical field (not direct contact)

Lightning Large static discharge between the earth and clouds. Lightning was found to be static electricity by Ben Franklin. Grounding Conductive path to Earth. Lightning rods & plumbing.

The electroscope can be used to detect electric charge

Electricity that moves… Current: The flow of electrons from one place to another. Measured in amperes (amps) Kinetic energy The amount of electric charge is measured in coulombs. 1 coulomb is the charge carried by 6.24 x 10^18 e¯. 1 amp (A) is 1 coulomb per sec (C/s)

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

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

Electric Current The reason electric charge flows from one place to another is voltage. Voltage is the difference in electrical potential between two places where e¯ are flowing. Voltage is the “push” that makes electric charges move. Measured in volts (V). HIGH LOW

Batteries Batteries are e¯ pumps. They provide a voltage difference to a circuit. Types: wet-cells & dry-cells

Kirchoff’s Laws Kirchoff’s First Law states that current entering a junction is equal to the current leaving the junction. Kirchoff’s Second Law states that the sum of the voltage drops around a complete circuit loop or path is equal to the applied voltage to 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.

Resistance = Voltage / Current Ohm’s Law Resistance = Voltage / Current Ohms = Volts / Amps Where: Current = I Voltage = V Resistance = R

Practice with Ohm’s Law Volts Amps 4 100 25 15 150 10 2 30 9 45 5 6 48 8

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 !!!!