Chapter 7 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

Warmup What is Electricity? What is a Positive Charge? What is Static Electricity? What is the Law of Conservation of Charge?

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

Electricity Transferring Electric Charge 2.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 3.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.