chapter 32 notes i

Chapter 32 Notes I

Electrical Charge- Electrostatics

What does it mean if something has a charge?

Charges are physical properties of matter

What is a static charge?

charges at rest. Electrical forces are much stronger than gravity

but the repel each other, however they are still acting on you at all times.

Can be positive and negative. Mythbusters vandegraff

Like charges repel and unlike charges attract. Neutrals are attracted to all charged objects. Charges exert a force through a distance. The two charges are considered to be opposite,

because an object with equal amounts of positive and negative charge has no net charge.

Electrical Forces are much stronger than gravity…

Why don’t we notice them?

The attractive and repulsive forces between the charges in Earth and the charges in your body balance out!!!!

Charge and the Atom

What 3 subatomic particles are the atom made of?

What is the charge of each?

Electromagnetic force is significant at atomic level. Things you know:Atom has positively charged nucleus

surrounded by negatively charged electrons

All electrons are identical (same mass; same quantity of negative charge)

All protons are identical (same mass; same quantity of positive charge)

Nucleus composed of protons and neutrons. Neutrons are neutral

Neutral atoms have equal protons and electrons so zero net charge

Reviewing what you already know…

Do metals tend to gain or lose electrons? Lose Do atoms lose or gain protons? no What is an atom called that does not have

equal numbers of protons and electrons? ion If electrons are in excess the net charge is? Negative If protons are in excess the net charge is? positive

Conservation of Charge The total amount of charge in the universe is

constant Charges cannot be created or destroyed – only

transferred. Electrons cannot be created or destroyed – only

transferred.

Conductors Materials through which electric charge

can flow Outer electrons are loose METALS, water, human body, salts Head rush Human conductors

INSULATORS Electrons are tightly bound and

remain with particular atoms. – not free to wander

Poor conductors of electricity RUBBER, GLASS, styrofoam, paper

Random question… Does lightening ever strike the same

place twice?

SemiconductorsA third class of materials that

have electrical properties in between insulators and conductors.

Germanium and siliconSometimes act as insulators and

sometimes as conductors

Transferring Charges Electric charges can be transferred by

1. Friction2. Contact3. Induction

Charge by Friction Transfer of electrons between two

objects that are touching. Electrons will travel to the object that

has the higher electron affinity (love for electrons)

Charge by Contact Both insulators and conductors can be

charged by contact. Contact occurs between charged object

and neutral object. These two objects will then have the same charge.

Involves transfer of electrons

Charge by Induction If a charged object is brought near a

conducting surface, even WITHOUT physical contact, electrons will move to the conducting surface.

Involves rearrangement of electrons

Charging by induction occurs during thunderstorms. The negatively charged bottoms of clouds induce a positive charge on the surface of Earth below. Most lightning is an electrical discharge between oppositely charged parts of clouds. The kind of lightning we are most familiar with is the electrical discharge between clouds and oppositely charged ground below.

Grounding When we allow charges to move off (or

onto) a conductor by touching it, it is common to say it is grounded.

Charge by Induction If this source is connected to the earth

by conducting wire or pipe (grounded), the electrons will move into or out of the substance.

1. If a neutral atom has 22 protons in its nucleus, the number of surrounding electrons is

a. less than 22.b. 22.c. more than 22.d. unknown.

Assessment Questions

1. If a neutral atom has 22 protons in its nucleus, the number of surrounding electrons is

a. less than 22.b. 22.c. more than 22.d. unknown.

Answer: B

Assessment Questions

2. When we say charge is conserved, we mean that charge can a. be saved, like money in a bank.b. only be transferred from one place to another.c. take equivalent forms.d. be created or destroyed, as in nuclear reactions.

Assessment Questions

2. When we say charge is conserved, we mean that charge can a. be saved, like money in a bank.b. only be transferred from one place to another.c. take equivalent forms.d. be created or destroyed, as in nuclear reactions.

Answer: B

Assessment Questions

4. Which is the predominant carrier of charge in copper wire? a. protonsb. electronsc. ionsd. neutrons

Assessment Questions

4. Which is the predominant carrier of charge in copper wire? a. protonsb. electronsc. ionsd. neutrons

Answer: B

Assessment Questions

5. When you scuff electrons off a rug with your shoes, your shoes are then a. negatively charged.b. positively charged.c. ionic.d. electrically neutral.

Assessment Questions

5. When you scuff electrons off a rug with your shoes, your shoes are then a. negatively charged.b. positively charged.c. ionic.d. electrically neutral.

Answer: A

Assessment Questions

6. When a cloud that is negatively charged on its bottom and positively charged on its top moves over the ground below, the ground acquires a. a negative charge.b. a positive charge.c. no charge since the cloud is electrically neutral.d. an electrically grounded state.

Assessment Questions

6. When a cloud that is negatively charged on its bottom and positively charged on its top moves over the ground below, the ground acquires a. a negative charge.b. a positive charge.c. no charge since the cloud is electrically neutral.d. an electrically grounded state.

Answer: B

Assessment Questions

7. When a negatively charged balloon is placed against a non-conducting wall, positive charges in the wall area. attracted to the balloon.b. repelled from the balloon.c. too bound to negative charges in the wall to have any effect.d. neutralized.

Assessment Questions

7. When a negatively charged balloon is placed against a non-conducting wall, positive charges in the wall area. attracted to the balloon.b. repelled from the balloon.c. too bound to negative charges in the wall to have any effect.d. neutralized.

Answer: A

Assessment Questions