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.