![Page 1: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/1.jpg)
Electricity and Magnetism
Physics 102Professor Lee
CarknerLecture 8
![Page 2: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/2.jpg)
Electricity and Magnetism
In E&M, we will deal with forces that depend upon charge
Charged particles generate E&M forces Stationary charges exert an electric force
E&M forces only affect charged particles
![Page 3: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/3.jpg)
Forces The electric force is much stronger than the
gravitational force
Why don’t we feel this strong force?
Most things have roughly equal numbers of positive and negative particles
Like charges repel, opposite attract Charges want to arrange themselves so there is no
force e.g. lightning, static electric shock
![Page 4: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/4.jpg)
Plus and Minus The basic particle of negative charge is the
electron The basic particle of positive charge is the proton
They are bound in the nucleus
Adding electrons makes something negative
All E&M forces depend on what the electrons are doing
![Page 5: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/5.jpg)
Using Electricity
Why is the electrical force important?
Convert electrical energy into work
Convert electrical energy into heat and light
Convert electrical energy into sound
Electrical energy can be very finely controlled Computer, internet
![Page 6: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/6.jpg)
Units of Charge The unit of charge is the Coulomb (C)
The electron and the proton have equal and opposite charges:
1 e = 1.60 X10-19 C
Charge is represented by the variable q (or sometimes Q)
![Page 7: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/7.jpg)
Electric Force
F = k q1 q2/r2
Where: k is the Coulomb constant (8.99 X 109 N m2/C2) q1 and q2 are the two charges (in Coulombs)
You must assign a sign to F at the end
r is the distance between them (in meters)
![Page 8: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/8.jpg)
Direction of Forces
but, to find the direction of the force we need to
use the rule:opposites attract, like repel
n.b., the direction of the force does not come out of the equation, you have to find it yourself
![Page 9: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/9.jpg)
Making Electricity
Three ways to do this Chemically
e.g. Magnetically
e.g. Physically
Four basic methods: friction, conduction,
induction, polarization
![Page 10: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/10.jpg)
Triboelectricity
Rubbing will transfer electrons from one substance to the other by friction
Example: Glass rubbed with silk becomes positive, rubber rubbed with fur becomes negative
![Page 11: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/11.jpg)
Fur Rubber
e-
Rubbing a piece of rubber with fur transfers the electrons from the fur to the rubber due to friction.
Triboelectric Charging
![Page 12: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/12.jpg)
How Does Charge Move?
Conductors When you charge a conductor, the electrons will flow
through it
Other types do not allow electrons to flow (e.g. glass, rubber) Insulators
If you charge them, the charge stays put
![Page 13: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/13.jpg)
Conduction
Both end up with the same sign charge
Example: shocking your friend
![Page 14: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/14.jpg)
Neutral Metal
Charged Metal
e-
Charge will move from one conductor to another
Conductive Charging
Both Metal Rods Now Charged
![Page 15: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/15.jpg)
Induction
attract the opposite sign charges to the near end
The whole conductor has no net
charge, but each end does Will always attract the original charged
object
![Page 16: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/16.jpg)
Induced Charge on Metal
Charged Metal
A charged conductor will split the charge on a near-by conductor
Inductive Charging
![Page 17: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/17.jpg)
Induction via Grounding If you connect a conductor to the Earth, an
endless amount of charge can flow from it to the ground
If you place a charged object near a grounded conductor it will repel the same sign charges to the ground
Charge is opposite that of the inductor
![Page 18: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/18.jpg)
Metal becomes positive
Charged Metal
A charged conductor will push out the same charge to the ground, leaving the other conductor with an opposite charge
Inductive Charging with Grounding
Electrons pushed to ground
![Page 19: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/19.jpg)
Polarization
You have charged the balloon but not
the wall The negative charge on the
balloon attracts the positive charged parts of the molecules of the wall, polarizing it
![Page 20: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/20.jpg)
Polarization
![Page 21: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/21.jpg)
Origins of Electricity Moving charges by
rubbing has been known since ancient times
Benjamin Franklin proposed the terms positive and negative for the two types of charge
![Page 22: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/22.jpg)
Franklin’s Kite Franklin
demonstrated that lightning is a form of electricity
He flew a kite in a thunderstorm and saw that charge flowed down the string
![Page 23: Electricity and Magnetism Physics 102 Professor Lee Carkner Lecture 8](https://reader035.vdocuments.mx/reader035/viewer/2022081504/56649d485503460f94a22dc5/html5/thumbnails/23.jpg)
Next Time
Read: 16.5-16.7 Homework: Ch 16: P 8, 12, 23, 24