142 Quiz 1

Question 1

What are the two forms of electric charges?

Answer 1

proton and electron

Question 2

Are electric charges created or destroyed?

Answer 2

no, we just move them around

electric charges

Question 3

Does anything truly have no charge?

Answer 3

no, a neutral object just has the same number of positive and negative charges

Question 4

Conductor

Answer 4

at least some of the charges are free to move about within the material

Question 5

Examples of conductors

Answer 5

ions in water and metals

Question 6

Insulator

Answer 6

charges do not move freely / charges are stuck to molecules

Question 7

Examples of insulators

Answer 7

plain water, wood, plastic, glass

Question 8

Charging by induction

Answer 8

start with electrically neutral material and bring a charged material near it (not touching)

the like-charges repel away and can connect another wire to the ground

like-charges want to get far away from the charge so will move into the ground

disconnecting the ground wire will make the neutral object have the opposite charge of the charged object near it

Question 9

Why do you have to disconnect ground wire first in charging by induction?

Answer 9

if instead you would have removed the charged object, the charges would have just migrated from the ground into the object to return to neutral

Question 10

Charging by conduction

Answer 10

touch a charged object to a neutral object

charges migrate to the neutral object and the neutral object becomes charged

Question 11

How do you determine the direction of the electric force using Coloumb’s law?

Answer 11

Don’t actually use Coloumb’s law, instead you use attract/repel with a coordinate system

Question 12

principle of superposition

Answer 12

the net force acting on a charge is the vector sum of the forces acting on it

Question 13

Why are neutral objects attracted to charged objects?

Answer 13

the charged object pulls the opposite charges of the neutral object towards it and pushes the like charges away from it

overall, the opposite charges interact at a shorter distance (since going towards it) so they have a stronger force

this makes the attractive forces overcome the repulsive forces and the charged object is attracted to the neutral object

Question 14

Do test charges influence electric field?

Answer 14

No! The charge at a point in space does not influence the electric field exactly at that point

Question 15

What is a field?

Answer 15

a quantity that has a value everywhere in space

can be a scalar or a vector field

Question 16

What direction do electric fields point for positive charges?

Answer 16

Away from positive charges

Question 17

What direction do electric fields point for negative charges?

Answer 17

Towards negative charges

Question 18

How do positive charges feel forces from electric fields?

Answer 18

In the same direction as the electric fields

Question 19

How do negative charges feel forces from electric fields?

Answer 19

Feel a force in the opposite direction of the electric field

Question 20

What are the units of an electric field?

Answer 20

N/C

Question 21

What represents the strength of an electric field?

Answer 21

the density of lines

Question 22

What represents the direction of an electric field?

Answer 22

direction is tangent to the lines of E

Question 23

Electric fields in conductors

Answer 23

electric field will create areas in the conducting sphere of more negative charge and areas with more positive charge

the area of more negative charge will create its own electric field in the opposite direction

over time, the field from charge separation will cancel out the original field and there will be no field in the conducting sphere

Question 24

In general, what is the electric field in a conductor?

Answer 24

0

Question 25

Electrostatics

Answer 25

case where nothing is changing over time

an example is inside a conducting sphere

Question 26

What happens inside a conducting sphere?

Answer 26

1) E=0
2) any excess charge on sphere can’t be inside the sphere, excess charge is found on the surface
3) E at surface of sphere is always perpendicular to surface
4) Charge accumulates at sharp points on an irregular surface

Question 27

What happens when a neutral object is brought near a Vandegraff generator?

Answer 27

the neutral object is initially attracted to the negatively charged generator

then, the generator transfers charge to the neutral object when close enough

the neutral object is now likely charged and will be repelled from the generator

Question 28

Flux

Answer 28

measure of how much of the electric field vectors penetrate through a given surface

Question 29

Gauss’s law

Answer 29

a technique for calculating the avg electric field on a closed surface

Question 30

What angle do we use for Gauss’s law?

Answer 30

angle between the Normal Surface and the Electric Field line

Question 31

Where do we place the Normal Surface?

Answer 31

kind of at the tail of the electric field line

makes more sense with a picture

normal surface is perpendicular to the material’s surface

Question 32

For a closed surface through which net flux is zero which statement must be true?

Answer 32

the net charge inside the surface is 0

electric field lines entering the surface matches the electric field lines leaving the surface

E*A = Qinside/episolon not