Physics Study Guide - Electrostatics and Electric Field

1. What is the charge of an electron? A proton?

Negative; positive

2. When something gets a negative charge are electrons gained or lost? When something gets a positive charge are electrons gained or lost?

Gained; lost

3. Describe the atoms/electrons in a conductor. Give an example of a conductor.

Free electrons, can move throughout the material. Example: any metal

4. What is different about the electrons in an insulator? Example?

Electrons are bound to their atom, can move very little. Example: rubber, glass, plastic, wood,

cloth

5. If two surfaces rub across each other and one of them gains electrons, this is charging by _____. Give an example

Friction; balloon and hair

6. If a charged object TOUCHES (comes in contact) with another object and gives it a charge, this is charging by ____. Give an example.

Conduction; touching the Van de Graaff, touching a charged car and getting a shock.

7. If a charged object is brought NEAR an uncharged object and charges are removed from it, this is charging by ____.

Induction

8. A negatively charged balloon is brought near a neutral wall. Describe what happens.

Neg. charges in wall move back (repelled) leaving a + surface on the wall which attracts the

balloon (polarization)

9. A charged object is brought near a neutral, metal object. Is the metal attracted, repelled, or not affected?

Attracted (metal object is polarized)

.

10. Explain what causes lightning using the ideas of electric charge and polarization.

A charged cloud gets near the ground or building and polarizes it. Electrons are attracted to

polarized surface and jump to the object.

11. What does it mean when something is electrically "grounded" ?

A pathway for extra charges to get to the earth has been provided

12. What is the SI unit for charge?

Coulomb

13. Electric force is proportional to _____ and inversely proportional to _____.

Charge; distance

14. Compare Coulomb's Law to the Law of Gravity. Give two differences and two similarities.

Differences: gravity never repels while electric can repel, gravity depends on mass while electric

depends on charge.

Similarities: Both can attract, both are inversely proportional to distance squared.

15. If you double the distance between two charges, how is the force affected? What if you double one of the charges?

¼ of the force; 2 times the force

16. Find the electric force between a +0.5 C charge and a +0.012C charge that are 10 meters apart.

540,000 N

17. Explain what an electric field is and what the electric field lines show us.

Space around a charged object in which electric force can be felt; lines show us where the

force/field is strong and weak and what direction the force is in.

18. Draw the E-field lines between two electrons.

See board.

19. According to the electric field lines, how can you tell where the electric field is strongest and weakest?

Strongest - where lines are close together; weakest - where lines are spaced apart.

20. E-field lines always point away from _____ charges and toward ____ charges.

Positive; negative

21. What are the units for electric field? Force? Charge? Work?

N/C; N; C; J

22. Find the strength of the electric field where a 0.06 C charge feels a 15 N force.

E = 15/0.06 = 250 N/C

23. How much force does a 12 N/C electric field exert on a charge of 0.00026 C?

E = F/Q; F = EQ = 12 (0.00026) = 0.00312 N

Electrical forces between charges are normally

strongest when the charges are ____________.

close together.

To charge an object by induction, the charged

object will ____________.

Be brought near the other object.

Electrical polarization occurs when ____________.

charges in a neutral object separate.

**Two charged particles held close to each other are

released. As they move, the force on each particle

increases. Therefore, the particles have ____________.

opposite signs.

A positive charge and a negative charge held near

each other are released. As they move, the distance

between them ____________.

decrease

Coulomb's law says that the force between any

two charges depends ____________.

both A and B

When the distance between two charges is halved,

the electrical force between charges ____________.

quadruples.

If you comb your hair and the comb becomes

positively charged, your hair becomes ____________.

negatively charged.

A difference between electrical forces and

gravitational forces is that electrical forces include

____________.

repelling force.

In a good insulator, electrons are usually

____________.

tightly bound in place.

A Coulomb is a unit of ____________.

charge.

Nancy's hair stands out when she is touching the

charged Van de Graaff generator. The reason her hair

stands out is because ____________.

same charges repel.

The direction of electric field lines show the

____________.

direction of the force on a positive charge.

An electric field has ____________.

both A and B

In a good conductor, electrons are usually

____________.

free to move around.

Objects can be charged by ____________.

friction.

conduction.

induction.