Electricity & Magnetism Chapter 8 Student Learning Objectives Recall properties of charge Characterize static electricity Differentiate between series and parallel circuits Describe properties of magnets Analyze electromagnetic systems

These Practice Problems are presented in class What is charge? http://www.pond5.com/stock-footage/68580/atom5.html 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 These Practice Problems are presented in class Electric Vocabulary

Neutral atoms have the same number of electrons and protons. 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

Opposite charges  attract Objects become charged when they lose or gain electrons. (ionized) The electric force and the gravitational force are both inverse square laws, and both apply mutual forces between two quantities. Opposite charges  attract Like charges  repel Electric Force Gravitational Force Attract & Repel Attract Strong Weak F = k(q1)(q2) d2 k is a constant = 9.0 x 109 Nm2/C2 q = charge d = distance between charges

Repulsive and Attractive Electrical Forces Two negative charges repel Two positive charges repel One negative and one positive attract Repulse Repulse Attract Section 8.1

Practice These Practice Problems are presented in class

How do objects become charged? The Science of Static Electricity Electrons are lost or gained, or are redistributed within the object. Friction: electrons are “knocked loose” and transferred Contact: electrons are transferred Induction: charge is rearranged A net electric charge on an object results in static electricity. Examples: Cars & Clothes

Practice These Practice Problems are presented in class

What is an electric field? An electric field surrounds charge, modifying the space near the charge. An electric field explains the action-at-a-distance between charged objects. Charge affects the space around itself. Objects are affected by the field established in that space. Electric fields interact. Lines of Force http://www.physicsclassroom.com/class/estatics/u8l4c.cfm

What are the properties of electric circuits? Electric current is the net movement of electrons. Electrons are present in all electrical systems. When they begin to move, there is current. Current = I = q/t Two different electric potentials set-up an electric field, which causes existing electrons to flow from the high potential to the low potential. EPE → KE as charge is accelerated through the system. No difference in electric potential = no charge will flow. E Field  Current

Examples: Wall Outlets (ac), Batteries (dc), Lightening, "Shock War", Bird on a Wire Voltage is created by a difference in electric potential energy. Electric resistance is a measure how difficult it is for electrons to move within the system. Conductivity Length Diameter Temperature How do Batteries Work?

Simple Electrical Circuit The light bulb offers resistance. The kinetic energy of the electric energy is converted to heat and radiant energy. Section 8.2

Electrical Circuit & Waterwheel Analogy Section 8.2

Practice V = IR P = IV Ohms Law Power is the rate at which the electric energy is used by a system. V = IR P = IV V=Voltage (V) or Potential Difference I = Current (A) R = Resistance () P = Power (W) Practice These Practice Problems are presented in class How do Solar Panels Work?

These Practice Problems are presented in class

Series Circuit Rs = R1+R2+R3+… If one bulb were to burn out the circuit would be broken, and all the lights would go out Same current all the way Section 8.3

Current Divides, Voltage is the same Parallel Circuit I = I1+I2+I3+… for R in parallel: 1/Rp = 1/R1+1/R2+… for 2 R in parallel: Rp = (R1R2)/(R1+ R2) Current Divides, Voltage is the same Section 8.3

How are circuits wired? Series Circuits: single continuous loop Voltage is divided. (energy shared) Resistance is additive; it increases with each added piece. Parallel Circuits: multiple parallel loops Voltage is supplied to each parallel loop. (energy not shared) Resistance will drop; it decreases with each added piece. R = R1 + R2 + … 1 = 1 + 1 + … R R1 R2

What are the properties of the magnetic field? These Practice Problems are presented in class What are the properties of the magnetic field? All magnets have two poles; this is where the magnetic field is strongest. A north-seeking pole A south-seeking pole The poles are not charged!

Practice: Compare and contrast electric charges and magnetic poles. A magnetic field surrounds a magnet, modifying the space near the magnet. Like magnetic poles  repel Opposite magnetic poles  attract Practice: Compare and contrast electric charges and magnetic poles.

What produces magnetism? https://www.youtube.com/watch?v=hFAOXdXZ5TM&feature=youtu.be The motion of electric charge is what makes a material magnetic. Magnets: Intrinsic magnetic moments of the electrons align. (spin)

Wires: Electric current forces magnetic moments to align. Convection: ionized material in motion produces a magnetic field. I B-Field https://www.youtube.com/watch?v=yB0qYHkTWJ4

The Earth is surrounded by a magnetic field. Protects us from solar wind Produces aurora And the poles switch! http://www.scientificamerican.com/article/earth-s-magnetic-field-flip-could-happen-sooner-than-expected/ https://www.youtube.com/watch?v=sBWPCvdv8Bk

How are electric and magnetic effects related? Electric charge moving induces magnetism. Magnetic field changing induces current. E-Fields and B-Fields interact. 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 https://www.youtube.com/watch?v=d_aTC0iKO68

Motors/Generators Motors Current induces magnetism Magnetic fields interact Electric energy  Mechanical energy (Rotation) Generators Magnetic field induces current Coils turned in B Field Mechanical energy  Electrical Energy Generators do not create energy, they convert it!

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

V2 = N2 V1 N1 These Practice Problems are presented in class Electric transformers transform the voltage.   Step down: fewer turns in secondary Step up: more turns in secondary V2 = N2 V1 N1 These Practice Problems are presented in class