Oct. 15 – Charging by Contact

Welcome back to class!  I hope everyone had a good long weekend.
We started with a bit of review to see if you remember what we did last week.  You should be able to identify what happens to charged objects and how they will behave.

Will these two objects attract, repel or not move at all?

Answer: The electrons (– charge) will move to one side and the overall result is that they will attract!

Charges can sometimes move around inside a neutral object and overall the two objects will attract.

Today we asked the question: How do objects become charged?

Learning Goals: Understand how objects gain or loose charge.

Success Criteria: You can identify how an object will be charged after contact or friction with another object.

How do Objects Get Charge

Charging by contact: 2 methods

 - Friction

 - Conduction

FRICTION

Rubbing two neutral materials together.

One loses electrons while one gains electrons.

How do we tell which one is positive or negative?

  - Electrostatic Series, P. 473

Ex: A cat plays in your hair.  Which one becomes positive?

A) Cat

B) Hair  <-- positive

C) neither

D) Don't know

How can I make two balloons attract each other?

- Rub one balloon on hair, balloon becomes negative.

- Rub the other balloon on polyester, it becomes positive.

- Since the charges are opposite, they balloons will attract each other.

CONDUCTION

A charged object comes in contact with another object.  Charges move around.

NOTE: ONLY electrons move.

 - The object that is MORE negative will lose electrons.

 - After contact, they will have the same charge.

The green shape is MORE negative, so it loses electrons.

The blue shape is MORE negative, so it loses electrons.

GROUNDING

A charged object comes into contact with a large reservoir of charge.   The charged object becomes neutral.

Ex: Your hand is charged.  You touch a doorknob, you lose charge to the door.

Ex: A balloon sticks to your hair.  You touch the balloon to the floor.  The balloon no longer sticks.

Homework

Read these sections in your textbook to see how electric charges can be applied.

• Electrostatic Paint Sprayers: P. 470
• Electrostatic Dusters: P. 475
• Electrostatic Precipitators: P. 476

Answer these Questions

• P. 477 #1-3, 5, 6