Electricity & Magnetism Chapter 8 Images: Creative Commons

Student Learning Objectives Compare and contrast electric and magnetic properties Characterize charge & static electricity Differentiate between series & parallel circuits Describe properties of magnetic materials Analyze electromagnetic systems

What is charge? All matter is composed of atoms which contain charged particles. electron proton neutron Charge − 1 + 1 –1.6 x 10−19 C +1.6 x 10−19 C Mass 9.1 x 10-31 kg 1.67 x 10–27 kg 1.67 x 10-27 kg http://www.pond5.com/stock-footage/68580/atom5.html

Practice Why do the electrons stay in orbit around the nucleus? Does an object that has lost electrons have a positive or negative charge? Does it have more or less mass? What is the charge in Coulombs, of an atom that has lost 2 electrons?

2 He 4.00260 Law of conservation of charge: The total amount of electric charge in the universe remains constant. Charge is never created or destroyed. Neutral atoms have the same number of electrons and protons. 2 He 4.00260 Atomic Number

Coulomb’s Law F = k(q1)(q2) d2 Objects become charged when they lose or gain electrons. (ionized) F = k(q1)(q2) d2 Image: Creative Commons

Practice Compare and contrast the electric force with the gravitational force. What is the electric force between the electron and the proton in a hydrogen atom? What is the gravitational force between these two particles? The average separation between the electron and proton in the hydrogen atom is 5.29 x 10−11 m.

More Practice Rubbing a balloon on your hair results in the transfer of 2000 electrons from your hair to the balloon. What is the force between your hair and the balloon if the balloon is 2 cm from your hair?

How do objects become charged? Electrons are lost, gained, or redistributed within a charged object. Friction: electrons are “knocked loose” Contact: electrons are transferred Induction: charge is rearranged

Image: sci-culture.com http://www.sci-culture.com/advancedpoll/GCSE/frictionandinduction.html Image: sci-culture.com https://phet.colorado.edu/en/simulation/balloons

Static Electricity Cars, Clothes, & Hair A net electric charge on an object results in static electricity. Cars, Clothes, & Hair Image Credit: Creative Commons

Practice Is an object that has been charged by induction ionized? A positive net charge results in static electricity. True b) False Static electricity on clothes and us is less common on humid days. Why? Why does a plastic slide retain static charge while a metal slide does not?

What is an electric field? An electric field surrounds charge, modifying the space near the charge. Objects within that space are affected. Image Credit: Creative Commons

Electric Fields Interact http://www.physicsclassroom.com/class/estatics/u8l4c.cfm Image Credit: Physicsclassroom.com

Practice What would the electric field lines look like between two equal positive charges? How would the electric field lines between two equal negative charges compare to the equal positive charges? Is there always an electric field surrounding charge?

https://www.youtube.com/watch?v=y9fgfQ078wc Doodle Science

What are the properties of electric circuits? Electric current is the net movement of electrons. Electrons are present in all electrical systems. When electrons begin to move in the same direction, there is current.

Volts = Joules/Coulomb Electric Potential Electric Potential is the electric potential energy between points A and B, for a charge q. Two different electric potentials set-up an electric field, which causes existing electrons to flow from the high potential to the low potential. Volts = Joules/Coulomb Potential Difference  E Field  Current

"Shock War“ Bird on a Wire Wall Outlets (ac) Batteries (dc) Lightening No difference in electric potential = no current. "Shock War“ Bird on a Wire EPE → KE as charge is accelerated. Wall Outlets (ac) Batteries (dc) Lightening

Electrical Systems Voltage is created by a difference in electric potential. Electric resistance is a measure how difficult it is for electrons to move within the system. Conductivity Length Diameter Temperature

Voltage & Power V = IR P = IV Ohms Law Power is the rate at which electric energy is used by a system. V = IR P = IV

Practice A flashlight uses a 1.5 volt battery and has a resistance of 2 ohms. What is the current within the flashlight circuit? How many Watts will this flashlight supply? A 2000 Watt hair dryer, a 100 Watt radio, and five 60 Watt light bulbs are being used simultaneously. Will this cause a 12 A safety switch to open? Assume the voltage supplied is 110 volts.

The current average utility rate is 26¢/kWh. More Practice An Xbox 360 console is attached to a 55 inch plasma TV. Each of these devices uses about 135 Watts. If you play the Xbox 360 on this TV for 4 hours, what is the cost? The current average utility rate is 26¢/kWh.

Life Practice A person with dry skin has a maximum resistance of 500,000 ; moist skin has a resistance of 1000 . If the metal prongs of a plug are touched as the plug is placed into a 110 volt wall outlet, how much current could pass through the person’s body? Is this dangerous? Don't try it! 0.001 A Noticeable 0.005 A Painful 0.010 A Muscle spasms 0.015 A Loss of muscle control 0.070 Disrupts heartbeat

How are circuits wired? Image Credit: ClipartFox.com

Series Circuits Parallel Circuits R = R1 + R2 + … 1 = 1 + 1 + … Single continuous loop Voltage is divided. (energy shared) Resistance is additive. (increases) Multiple parallel loops Voltage is supplied to each parallel loop. (energy not shared) Resistance will drop. (decreases) R = R1 + R2 + … 1 = 1 + 1 + … R R1 R2

Questions What do you think an electrical switch does within the circuit? Why is too much current in a wire dangerous?

What are the properties of the magnetic field? All magnets have two poles; this is where the magnetic field is strongest. North Seeking & South Seeking The poles are not charged! Stock Image

Magnetic Fields A magnetic field surrounds a magnet, modifying the space around the magnet. Images: Creative Commons

Practice Which poles of a magnet are attracted to each other? Which repel? How do electric charges and magnetic poles compare and contrast? How do electric fields and magnetic fields compare and contrast?

What produces magnetism? https://www.youtube.com/watch?v=hFAOXdXZ5TM&feature=youtu.be Video by Minute Physics

Magnetic Moments The intrinsic magnetic moments of electrons align creating magnetic regions called domains. Non-Magnetic Material no domains Magnetic Material domains not aligned Magnet domains aligned Image Credit: http://montessorimuddle.org

Electric Current Electric current forces magnetic moments to align. Current Carrying Wire Coil of Wire (Solenoid) Images from Creative Commons

Motion of Ionized Fluid Ionized fluid motion, in Earth’s outer core, produces a magnetic field that surrounds Earth. Rotation strengthens the field. Dynamo Effect

Protects us from solar wind Fun Facts Protects us from solar wind Produces aurora And the poles switch! Image Credit: NASA http://www.scientificamerican.com/article/earth-s-magnetic-field-flip-could-happen-sooner-than-expected/

https://www.youtube.com/watch?v=sBWPCvdv8Bk By Terje Sorgierd

Practice In general, what produces magnetism? Where are electromagnets used? Where is Earth’s magnetic field generated? If Earth had a faster rotation, how would this change the magnetic field?

How are electric and magnetic effects related? Electric charge moving induces magnetism. Magnetic field changing induces current. E-Fields & B-Fields Induce Each Other

Flashlights (no batteries required) Stock Images

Radio (no batteries required) Stock Image

Electromagnets (magnetism from electricity) Stock Images

More Loops + Turning Faster = More Voltage Faraday’s Law Faraday’s Law: Induced voltage in a coil is proportional to the number of loops, multiplied by the rate at which the magnetic field changes. More Loops + Turning Faster = More Voltage

Practice Do electric generators create energy or convert energy? Use Faraday’s law to explain how an electric generator works.

Maxwell’s Law DCurrent = Magnetism Maxwell’s Law: A magnetic field is induced in any region of space in which an electric field is changing with time. DCurrent = Magnetism

Electric Transformer V2 = T2 V1 T1 The relative number of turns determines the change in voltage. V2 = T2 V1 T1

Practice If a laptop needs only 12 volts and the wall outlet supplies 110 volts, what is the relative number of turns needed in each coil? Is the laptop transformer a step-up or step-down transformer? Apply both Faraday’s law and Maxwell’s law to the electric transformer?