Oct. 10 – Charges

New Unit: Electricity!

First of all, what is electricity?  Here's an example of electricity in nature:

Learning goals: Understand how to describe charge.

Success Criteria: You can use the idea of charges and static electricity to explain different situations.

Definitions
Electricity: The movement of charges.
Charges: An intrinsic property of matter.

• Electrons are negatively charged, –
• Protons are positively charged, +
• Neutrons have no charge, 0

You can not see or feel charge, you can only tell how it interacts with other charges.

Law of Electric Charges

• Like charges repel
       (+ repels +)
       (– repels –)
• Opposite charges attract
       (+ attracts –)
       (– attracts +) 

Static Electricity 

When charges accumulate on an object.

• An object with more electrons than protons becomes negatively charged.
• An object with fewer electrons than protons becomes positively charged.
• An object with the same number of electrons and protons is neutral.

We used the idea of charges attracting and repelling to explain what happens in these situations:

Charges accumulate in his hair.  All the charges are the same, so each hair repels the others.

The cat and ballon have opposite charges, so they attract each other.

Cat vs. Ballon Video: http://www.youtube.com/watch?v=TE2r0vjkXK0

Charges accumulate on the finger and jump to the door nearby.

This person uses the charges from the carpet going through his body to create a light show.

Static Wizard video: http://www.youtube.com/watch?v=8OePt0fSjqs

Finally we discussed the idea of induced charges.

Induced charge:

When a charged object comes near a neutral object, charges can separate in the neutral object.

I used an electroscope to demonstrate induced charges.

I also showed you how you can induced charges in water.

A similar experiment to what I showed you in class.

Homework

• P. 471 #2-7

Have a great Thanksgiving weekend!