Electricity and Electricity and MagnetismMagnetism

Chapter 7 OverviewChapter 7 Overview

ElectricityElectricity

Charge of proton PositiveCharge of proton Positive Charge of electron NegativeCharge of electron Negative Charge of neutron NONECharge of neutron NONE Static electricity- buildup of negative Static electricity- buildup of negative

charge on an object charge on an object Excess electrons on an objectExcess electrons on an object Very short electric dischargeVery short electric discharge

ElectricityElectricity

Why you end up with a static shock Why you end up with a static shock after walking across the carpet: after walking across the carpet:

Atoms in the carpet hold their electrons Atoms in the carpet hold their electrons more loosely than atoms in your shoesmore loosely than atoms in your shoes

Shoes gain electrons from the carpet, Shoes gain electrons from the carpet, becoming negatively chargedbecoming negatively charged

Carpet loses electrons & becomes Carpet loses electrons & becomes positively chargedpositively charged

Shock occurs when electrons are suddenly Shock occurs when electrons are suddenly transferred from one object to another- transferred from one object to another- this appears as a sparkthis appears as a spark

ElectricityElectricity

Charge is always conserved.Charge is always conserved. If one object is negative, another must If one object is negative, another must

be positivebe positive Conductors- substances through Conductors- substances through

which electrons move easilywhich electrons move easily Mostly metals and ionic solutionsMostly metals and ionic solutions

Metals conduct well because: atoms Metals conduct well because: atoms in metals have electrons that move in metals have electrons that move easily through the material easily through the material

ElectricityElectricity

Insulator- a material that doesn’t allow Insulator- a material that doesn’t allow electrons to move through it easily electrons to move through it easily Occurs because electrons are held tightly Occurs because electrons are held tightly

to the atoms in insulating materials to the atoms in insulating materials Charging by contact- the process of Charging by contact- the process of

transferring charge by touching or transferring charge by touching or rubbing two objects togetherrubbing two objects together

Charging by induction- rearrangement Charging by induction- rearrangement of electrons on a neutral object by a of electrons on a neutral object by a nearby charged objectnearby charged object

ElectricityElectricity

Voltage difference- push that causes Voltage difference- push that causes charges to move- measured in volts charges to move- measured in volts

Electric current- The flow of Electric current- The flow of electrons through a wire or any electrons through a wire or any conductor. conductor. Units of Amperes (A) Units of Amperes (A) Different from static electricity because Different from static electricity because

it lasts longerit lasts longer Some materials, like insulators, have Some materials, like insulators, have

resistance to flow of electric currentresistance to flow of electric current

Electrical CircuitsElectrical Circuits

Less resistance means less heat, which is Less resistance means less heat, which is safer for use in your homesafer for use in your home

Ohm’s law- current in a circuit equals the Ohm’s law- current in a circuit equals the voltage difference divided by the voltage difference divided by the resistance. resistance. I = V/R I = V/R

As resistance increases, current As resistance increases, current decreasesdecreases

As voltage difference increases, current As voltage difference increases, current increasesincreases

Electrical CircuitsElectrical Circuits Series circuit- current has only one loop Series circuit- current has only one loop

to flow through to flow through Parallel circuit- current has more than Parallel circuit- current has more than

one loop to flow throughone loop to flow through Magnetic fields form around wires Magnetic fields form around wires

through which electricity is movingthrough which electricity is moving Electromagnet- a temporary magnet made Electromagnet- a temporary magnet made

by placing a piece of iron inside a current-by placing a piece of iron inside a current-carrying loop of wire carrying loop of wire More loops = strongerMore loops = stronger More voltage = strongerMore voltage = stronger Only works for DC currentOnly works for DC current