Chapter 7 Electricity

Electricity An atom is the basic unit of matter and is made of protons, neutrons, & electrons protons: + charge electrons: - charge neutrons: no charge

Electricity An atom is the basic unit of matter and is made of protons, neutrons, & electrons when atoms contain the same number of protons & electrons they have a neutral charge positive charge – occurs when electrons are lost from atoms to other objects negative charge – occurs when electrons are gained from atoms of other objects

Electricity positive charge – occurs when electrons are lost from atoms to other objects negative charge – occurs when electrons are gained from atoms of other objects

Electricity static electricity – the accumulation of excess electric charges on an object example: as you walk on carpet, some electrons that are loosely held by the carpet are transferred to your shoes creating opposite charges

Electricity law of conservation of charge – states that charge can be transferred from object to object, but it can’t be created or destroyed similar to the law of conservation of mass or the law of conservation of momentum

Electricity Like & Opposite Charges opposite charges attract like charge repel

Electricity Conductors and Insulators Electricity is caused by the movement of electrons, from a negative to a positive region conductors - materials in which electrons can move through easily examples: metals & water responsible for shocks when an excess of electrons are transferred from one surface to another, such as from your hand to a doorknob

Electricity Conductors and Insulators Electricity is caused by the movement of electrons, from a negative to a positive region  insulators - materials in which electrons cannot move through easily examples: wood, plastic, rubber, & glass

Electricity Transferring Electric Charge charge by contact – the process of transferring charge by touching or rubbing causes a transfer of electrons from one object to another, leaving one object with a positive charge and the other one with an equal amount of negative charge example: socks being attracted to each other when coming out of the dryer because of rubbing during drying touching a door handle and getting shocked

Electricity Transferring Electric Charge charge by contact – the process of transferring charge by touching or rubbing

Electricity Transferring Electric Charge charging by induction – rearranging of electrons on a neutral object caused by a nearby charged object example: bringing a negatively charged balloon near clothing and having it cling to the clothing by an electrical force

Electricity Transferring Electric Charge lightning - caused by a large static discharge of electrons through the air that meet with the positive charge that is built up on the ground collisions of atoms and molecules in the air during this discharge account for light being given off

Electricity Lightning

Electricity Lightning

Electricity Transferring Electric Charge 4. thunder - sound wave generated by lighting the heat from lightning causes air to expand rapidly, producing sounds waves that you hear as thunder

Electricity grounding – a way to transfer any excess electric charge to the ground before it builds up and creates lightning examples: lightning rods, pipes, plumbing fixtures, metal faucets, etc.

Electricity The presence of electric charges can be detected by a device called an electroscope

Electricity 7.2: Electric Current How is it that electrons can move from one object to another or move through an object? The answer lies with a difference in voltage

Electricity voltage difference – the push that causes electrical charges to flow through a conductor measured in volts (v) Just how heat moves from a high temperature area to a lower temperature area, charge flows from a high voltage area to a low voltage area

Electricity circuit – closed, conducting loop through which an electric current can flow If the circuit is not closed, the electrons would have nowhere to go, just as if a water line broke, the water would not be able to flow through the pipe.

Electricity electric current – the flow of electric charge through a wire or any conductor electric current is measured in amperes (A)

Electricity Types of Batteries dry cell - involves a chemical reaction between zinc and a chemical paste that cause the central carbon rod to become positive and the surrounding lower region to become negative once the two terminals are connected through a circuit, electricity flows these types of batteries are the most common type (in flashlights or calculators)

Electricity Dry Cell Battery

Electricity Types of Batteries wet cell - involves two metal plates and typically an acid solution with a “bridge” these types of batteries are used in cars

Electricity resistance – the tendency for a material to oppose the flow of electrons, changing electrical energy into thermal energy and light resistance means, how hard it is to get electricity through resistance in measured in ohms () all materials have some electrical resistance electrical conductors have much less resistance than insulators

Electricity resistance – the tendency for a material to oppose the flow of electrons, changing electrical energy into thermal energy and light list some factors that affect resistance in a wire Material of the wire, length of the wire, and thickness of the wire

Electricity Ohms’s Law – a formula that is used to measure the amount of voltage or current in a circuit V = I  R V: voltage (measured in V) I: current (measured in amps) R: resistance (measured in )

Electricity Ohms’s Law – a formula that is used to measure the amount of voltage or current in a circuit V = I  R  Calculate the voltage difference across a 25- resistor if a 0.3-amp current is flowing through it.