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

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: + - + + + - - + - + + + - - - + + - - -

Charged objects exert a force (a push or pull) on other charged objects. The force between charged objects is an electric force. The size of the force depends on the amount of charge and the distance between the objects.

An electric field is the region around a charged object where the force is exerted on another object (how far it reaches).

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.

Objects can be charged in 3 different ways: Friction – rubbing Conduction – direct contact Induction – through an electrical field (no contact)

The law of electric charges states that like charges repel (push away) and opposite charges attract.

Electric Discharge… Electric Discharge is the release of electricity stored in a source This can happen slowly (as with laundry fresh from the dryer) OR It can happen very quickly like lightning!

Electricity that moves… Electric Current: the rate at which charges pass a given point; flow of electrons from one place to another Measured in amperes (amps) Kinetic energy

There are 2 types of currents: Direct Current (DC) – Where electrons flow in the same direction in a wire. (batteries)

There are 2 types of currents: Alternating Current (AC) – electrons flow in different directions (back and forth) in a wire (outlet in your house)

A cell is a device that produces an electric current by converting chemical or radiant energy into electrical energy. Wet cells have liquid electrolytes (battery acid) while dry cells have solid, paste-like electrolytes.

A thermocouple is a device that converts thermal energy into electrical energy. A photocell converts light energy into electrical 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 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 is more than one path to the components. If the circuit is broken at any one branch, only the components (load) on that branch will turn off.

Parallel Circuit

Conductors vs. Insulators Conductors – material through which electric current flows easily. Insulators – materials that electric current can NOT flow through easily.

Examples Conductors: Insulators: Metal Water Styrofoam Rubber Plastic Paper

What is Resistance? The opposition to the flow of an electric current, producing heat. Measured in ohms. The greater the resistance, the less current gets through. Good conductors have low resistance.

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? Voltage is the potential difference between two points in a circuit. The greater the voltage, the greater the force or “pressure” that drives the charge through the circuit. Measured in volts.

Difference b/t Volts and Amps and Ohms Example – you could say that… Amps (current) measure how much water comes out of a hose. Volts measure how hard the water comes out of a hose. Ohms (resistance) would depend on the length and thickness of the hose.

As resistance increases, current decreases Ohm’s Law Voltage(V) = Current (I)*Resistance (R) Volts = Amps*Ohms As resistance increases, current decreases

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