Post on 29-Dec-2015
Charge Model
• Balloon and Scotch Tape Electroscope Lab
Balloon Lab
• Big Idea: There exist electrical charges which can repel/attract one another.
Up and atom!
• An atom is the smallest unit of a particular element.
• Atoms are made up of protons (+), neutrons (0), electrons (-).
Scotch Tape Lab
• Big Idea:– (+) and (+) OR (-) and (-) repel– (+) and (-) attract– (+) and (0) OR (-) and (0) attract
• Why does neutral attract both?– Balloons sim
1.17.14
Coulomb’s Law
Warm Up/Review
• Determine how the following net charges on objects would interact:– (+) and (+)– (0) and (-)– (-) and (+)
¢harge Unit$
Compare
US Currency
$
Electric Charge
Smallest Possible
UnitPenny
$0.01 =1/100th of a dollar
Elementary Charge (1 e)(electron or
proton)1e= 1.60 x 10-19 C
Practical Unit
Dollar$1 = 100 pennies
Coulomb1 C = 6.25x1018 e
Elementary Charge
• Elementary charge- the smallest possible unit of charge (an electron or proton)
• The net charge on an object MUST BE an integral multiple of this charge.
• For example: e= 1.60 x 10-19 C
q= (1.5)e= 2.40 x 10-19 C IS NOT ALLOWED
q= (2.0)e= 3.20 x 10-19 C IS ALLOWED
Notes
1.21.14
Electric Field vs. Gravitational Field
Electric Field
• The electric field is the direction that a positive test charge would go.• The electric field has units of N/C.
𝐄=k𝑞𝑟2
Electric Field Sketches
Partner Quiz
• Each group gets 2 questions to ask me.
Book Sample Problems
Book Practice Problems
• 1, 6, 7, 12, 23, 27, 28
1.23.14
• Force and Field Warm Up Question
Warm Up
What do you conclusively know about the charge of each?
Warm Up
What do you conclusively know about the charge?
Plate Lab
Practice
Practice
1.24.14: MC Warmup
Charging By Induction Lab
Faraday Cage
Faraday Cage
• http://www.youtube.com/watch?v=Zi4kXgDBFhw
Faraday Cage
• There is no electric field inside of a conductor.• All excess charge spreads itself out on the outside of the conductor.• This is why you’ll be safe if your car gets struck by lightning.• This is also why you get horrible cell phone/radio reception in tunnels and
elevators.
• There can be an electric field inside of an insulator.
1.27.14
• A conducting sphere has radius R. Which graph represents the Electric field vs. distance from the center of the sphere?
• Two metal spheres that are initially uncharged are mounted on insulating stands, as show. A negatively charged rubber rod is brought close to, but does not make contact with, sphere X. Sphere Y is then brought close to X on the side opposite to the rubber rod. Y is allowed to touch X and then is removed some distance away. The rubber rod is then moved far away from X and Y. What are the final charges on the spheres?
Book Practice
STOP
• Book problems from past two days.