ElectricityElectrostatics

Investigating Electric Charges• One of the most common effects of static

electricity occurs when you comb your hair on a day when the air is very dry.

• Static electricity causes clothes to cling together.

Activity• Choose a partner.• Get one balloon and blow it up.• Rub the balloon against your partner’s hair and

attempt to stick the balloon to any vertical surface.

• Was this task possible? Why or why not?• What was the overall affect of the balloon rubbing on

your partner’s hair?

Review•Protons – a positively charged subatomic particle

•Electrons – a negatively charged subatomic particle

•Neutrons – a neutral (no charge) subatomic particle

The Electrical Nature of Matter•Electricity – the circulation or movement of electrons

•Electrostatics – the study of static electric charge

•Electric charges – a negative or positive quantity of electricity that builds up on an object

•Static electricity – a charge on a substance that stays in the same place on an object

Electric Charge

• There are two kinds of electric charge: negative and positive.

•When two neutral substances are rubbed together; one substance always becomes negatively charged while the other becomes positively charged.

• Example: When a comb is rubbed with wool, the comb acquires a negative charge, while the wool acquires a positive charge.

The Law of Electric Charges

1)Like charges repel each other (charges that are the same)

2)Opposite charges attract each other.

3)Both Positive and Negative charged objects will attract most neutral objects.

*Opposites Attract and Likes Repel*

A Model for the Electrical Nature of Matter1. All matter is made up of submicroscopic particles called atoms.

2. At the center of each atom is a nucleus containing the positively charged proton and the neutral neutron.

3. A cloud of negatively charged electrons surrounds the nucleus.

4. Like charges repel each other; unlike charges attract each other.

5. Some elements will lose their electrons

6. In each atom, the number of electrons equals the number of protons.

7. If an atom gains an extra electron, the net charge is negative, and it is called a negative ion. If an atom loses an electron, the net charge is positive, and it is called a positive ion.

Charging Objects•There are three basic ways to build up static electricity and electrically charge an object

• Charging by Friction

• Charging by Contact

• Charging by Induction

Charging by Friction•Charging by friction – transferring an electric charge from one substance to another by a rubbing action.

•When someone walks across a carpet, the friction between the carpet and the person’s shoes produces a charge on both the person (negative) and the carpet (positive).

The Electrostatic SeriesAcetate

Glass

Wool

Cat’s fur, human hair

Calcium, Magnesium, Lead

Silk

Aluminum, Zinc

Cotton

Wax

Ebonite

Plastic (Polyethylene)

Carbon, Copper, Nickel

Rubber

Sulfur

Platinum, Gold

Gains

Electrons

- The electrostatic series shows how things become charged when they are rubbed together.

- Items at the top of this list hold electrons very weakly and tend to lose them and become positive

- Items near the bottom hold electrons very well and tend to gain them and become negative

Electrostatic Series Practice

Which substances would have the positive and negative charge if rubbed together?

A) Glass and SilkB) Cotton and RubberC) Your t-shirt and your catD)A wedding ring and a drinking cup

Transferring Charge by Contact• When charging by contact occurs, one object is already

electrically charged. The other object may or may not be charged as well.

Example: When you touch a doorknob, the electric charges on your body are shared with the doorknob very rapidly.

- This is why you get shocked…Example 2: In our balloon experiment yesterday the balloon was charged from friction…once the balloon was touched to the wall however, the charge was being shared with the wall

Induction

Charging by induction – transferring an electric charge from one substance to another without direct contact.

**This charge is only temporary.

Ex: Neutral dust particles are charged by induction when approaching a charged tv screen.

Why does Induction occur?

• The dust particle in question is neutral and contains an even amount of positive and negative charges.

•When this particle comes near a positively or negatively charged object the charges in the dust rearrange. The opposite charges are repelled and move away from the same charge and the like charges move to the outside…

• This rearranging of charges causes the outside of the particle to be attracted to the object even though the dust is still neutral.

• Turn to Pg.285 to see a diagram of this

Practice

•Answer questions •Pg.273: # 2 and pg.275: 3a, 4, 5

Insulators and Conductors•Electrical insulators – a substance in which electrons cannot move freely from one atom to another.

•Electrical conductor – a substance in which electrons can move freely from one atom to another.•Metals are good conductors

Discharging Electrically Charged Objects

• If a charged object has all the excess electrical charges removed, it is said to be discharged or neutralized.

•There are several ways to discharge or neutralize charged objects: •1) Grounding

Ways Static Electricity is discharged1) Grounding•When a charged object is grounded it shares its extra charges with the entire Earth.

Ways Static Electricity is discharged2) Discharge at a Point• Removing an electric charge by pushing electrons off the tip of a pointed conductor.• Often seen in aircraft

•What would happen when the electrons causing an electric charge meet at a point?

Other Ways to Discharge Objects

3) Exposure to air.

4) Exposure to light

5) Expose it to radioactivity.

Lightning• Lightning is part of a natural process of exchanging electric charges between the atmosphere and the Earth.

•When thunderclouds form, huge numbers of negative charges tend to concentrate near the bottom of the cloud.

•When the negative charge at the base of the cloud moves over tall objects, such as buildings, they can be discharged by grounding in a huge spark which creates the lightning we see.

Lightning Rods

•Direct the charge from lightning, when it does strike, towards the ground.