Electric Charges Two types of electric charges: – Positive = protons – Negative = electrons – If # of electrons = # of protons, neutral – More electrons, negative charge – More protons, positive charge

Examples of Static Electricity

Electric Charge Opposite charges attract – Static cling in a dryer – Example Shirt loses electrons (+) Socks gain electrons (-) Opposite charges attract and stick together Like charges repel

Law of Conservation of Charge Charge can be transferred, but not created or destroyed.

Conductors and Insulators Conductor – Material in which electrons (electricity) are able to move easily – Most metals Insulator – Material in which electrons do not flow easily – Rubber, plastic, glass and wood

Electric Charges Static Electricity – Build up of excess electric charges on an object – Objects either lose or gain electrons to carry a charge

Lightning – Large discharge of static electricity – Negative charges at bottom of cloud are attracted to positive charges on ground – Lightning Lightning

Charging Objects Charging by Induction – Rearrangement of electrons on neutral object – Caused by nearby object that is charged Charging by Contact – Transfer of electric charge by touching or rubbing

Charging by Induction

Charging by Contact

Electric Currents Electric Current – Movement of electric charges in a single direction – Measured in Ampere – 1 amp = 6,250 million billion electrons flowing past a point each second What is Electric Current? What is Electric Current?

Voltage Difference – Electric charges always flow from higher voltage to lower voltage – Voltage difference is the force that causes electric charges to flow – Measured in volts

Electric Circuits Circuit – Closed path that electric current follows – Path or circuit broken, electricity will not flow

Batteries – Provides the voltage difference in some circuits – Keeps current flowing through circuit – Dry cell or wet cell

Batteries Dry Cell – 2 electrodes surrounded by electrolyte – Electrolyte is a moist paste Wet Cell – The electrolyte solution is a liquid – Voltage Sources Voltage Sources

Resistance – Tendency of a material to oppose the flow of electrons – Conductors have a low resistance – Insulators have a high resistance – Measured in Ohms (Ω) – Electrical Resistance Electrical Resistance Resistance at the Molecular Level Resistance at the Molecular Level

Ohm’s Law – The relationship between voltage difference, current and resistance – Provides a way to measure the resistance of materials – I (current) = V (voltage) ÷ R (resistance) – I = V/R

Ohm’s Law Ohm's Law

Circuits Series circuit – Current has only one loop to flow through – Used in flashlights and some holiday lights – Disadvantage Any part of circuit is disconnected, electricity stops flowing

Circuits Parallel Circuits – Contains two or more branches for currents to move through – Homes, cars and most electrical systems use parallel circuits – Advantages Turn a light off, current continues to move through to other branches

Electric Power – Rate at which electrical energy is converted to another form of energy – Power = current x voltage difference – P = I x V – Unit of measurement is the kilowatt

Electrical Grids