Matter

• All matter is made of very small particles called atoms

• Atoms are composed of even smaller particles called protons (+), neutrons (no charge) and electrons (-)

• The attraction between protons and electrons is what holds the electrons in placed around an atom

• An atom is neutral if it has the same number of proton as it does electrons

Electricity

• Charge – a physical property that can be positive or negative

• Law of electric charge – like charges repel, opposite charges attract

• Force between charged objects if an electric field exist is called electric force

• 2 things affect electric force:– Amount of charge– Distance between the charges

• Electric field is the region around a charged object

• An object becomes positively charged when it loses electrons and negatively charged when it gains electrons

• Objects become charged by friction, conduction, induction

• Friction – when electrons are “wiped” from one object to another (rubbing your hair with a ballon)

•

• Conduction – electrons move from one object to another by contact

• Induction – charges in a uncharged metal object are rearranged without direct contact it a charged object

• Electrical conductor – material which allows charges to move freely

• Electrical insulator – material in which charges can’t move freely

• Static electricity – electric charge at rest on an object (static – not moving)

• Electric discharge is the loss of static electricity as the charge moves off the object

• Electric discharges can happen quickly with a flash of light, a shock, or a crackling noise (lightning)

• Electric current is the rate at which charges pass a given point (units amperes, A)

• When a current is established (turned on) an electric field is created so quickly (speed of light) that all electrons start moving through the wire at the same instant

• AC – (alternating current) the charges continually shift direction (plug outlets)

• DC – (direct current) the charges always move in the same direction (battery)

• Voltage is difference between two points in a circuit (units volts, V)

• Voltage is a measure of how much work is needed to move a charge between two points, the higher the voltage, the more energy released per charge (9V, 12V, 120V, 220V)

• Resistance is the opposition to the flow of charges (units ohms,Ω (R))

• The higher the resistance, the lower the current

• Resistance depends on the material, length, thickness and temperature

• Superconductor – super cooled material that lowers resistance (magnets)

• Device can change one form of energy to another such as thermocouples and photocells. Thermocouples change thermal energy into electric energy and photocells change light energy to electric energy

• Electric circuits are complete closed paths that allows electric charges to flow

• Three parts to a circuit are:

• 1. Energy source (provides electric charge)

• 2. Wires (allows charge to flow from point to point)

• 3. Load (changes electric charge into other forms of energy)

• EX: radio – electrical to sound

Batteries (power source)Dry Cell Wet Cell

• Two types of circuits: series and parallel

• Series: all parts are connects in a single loop in a one way path

• All current must pass through the complete series for circuit to work

• Any interruption causes the circuit to fail (Xmas lights)

• Useful in burglar alarms

Series Ciruit

• Parallel: loads are connected side by side and current can travel on more than one path

• When circuit is interrupted, circuit continues to function regardless

• Homes are wired on parallel circuits and can have different loads in the circuit

Parallel Circuit

• Circuit failures are usually caused by over loads or damage to the structure of the circuit

• Fuses and circuit breaks “fail over” and automatically break the circuit to protect circuit and property

• Electromagnets – temporary magnets that lose their magnetism when electric current is removed

• Electricity can produce magnet fields and can cause metals such as iron and steel to act like magnets

• Generator is a device that converts mechanical energy into electrical energy by using magnets and a coil of wire that creates magnetic fields

• Electric motors convert electrical energy into mechanical energy that is used to do work

• EX: motors in house hold appliances like blenders and washing machines