Chapter 20

Question 1

Like charges do what?

Answer 1

Like charges repel each other

Question 2

opposite charges do what?

Answer 2

opposite charges attract each other

Question 3

what does neutral mean?

Answer 3

an object has no charge or the net charge is zero

Question 4

what does charging mean (acquired charge)?

Answer 4

most things are electrically neutral, they have equal amounts of negative and positive charges. We can use certain materials to help them acquire charge. Most materials are divided into 3 categories

Question 5

what are the 3 categories of materials used to charge objects?

Answer 5

1. Charging by Friction
2. Charging by Contact
   3: Charging by Induction:

Question 6

what is charging by friction?

Answer 6

this is useful for charging insulators, if you rub one material with another, electrons have a tendency to be transferred from one material to the other

Question 7

what is charging by contact?

Answer 7

This is useful for charging metals and the conductors, If a charged object touches a conductor, some charge will be transferred between the object and the conductor, charging the conductor with the SAME sign as the charge on the object

Question 8

what is charging by induction?

Answer 8

Also useful for charging metals and other conductors, a charge object is brought near/close to the conductor and does NOT touch iT, if the conductor is on the ground electrons will either flow away from it or onto it. when the ground connection is removed the conductor will have a charge OPPOSITE in sign to that of the object

Question 9

what is electrical force?

Answer 9

the LONG-RANGE FORCE between charged objects, it can be repulsive or attractive
- gravity is another long-range force, but it is always attractive

Question 10

what are the two types of electric charges that exist?

Answer 10

1. positive (proton)

2. negative (electron)

Question 11

electric charge is always what?

Answer 11

electric charge is always conserved!

- objects become charged because negative charge is transferred from one object to another

Question 12

what is nature’s basic carrier of a positive charge?

Answer 12

The proton!

- protons do not move from one material to another because they are held firmly in the nucleus

Question 13

what is nature’s basic carrier of the negative charge?

Answer 13

The electron!

- gaining or losing electrons is how an object becomes charged

Question 14

electric charge is?

Answer 14

electric charge is QUANTIZED: it comes in units of the fundamental charge
unit : Coulomb (C)
e = 1.6x10^-19 C

Question 15

what is a conductor?

Answer 15

conductors are materials in which the electric charges move freely in response to an electric force.

• ie) metals; copper, aluminum and silver
• ADDED charge redistributes itself quickly over conductors

Question 16

what is an insulator?

Answer 16

insulators are materials in which electric charges do not move freely.

• ie) plastics; glass, rubber
• when insulators are charged by rubbing, ONLY the rubbed area become charged, hey don’t distribute themselves evenly

Question 17

what is electrostatic equilibrium?

Answer 17

• charges on an insulator do not move

- charges on a conductor adjust until there is no net force on any charge

Question 18

What is the Charge model?

Answer 18

The basic postulates of charges and charging

Question 19

what does ground/grounded mean?

Answer 19

basically anything neutral that give up electrons to, or take electrons from, an object

Question 20

what is Coulomb’s Law?

Answer 20

The electric force between two point charges:
- is directed along the line joining the two particles
- is inversely proportional to the square of the separation distance (r) between them
- is proportional to the product of the magnitude of the charges |q1| & |q2| on the two particles
- is attractive if the charges are of opposite sign and repulsive if the charges have the same sign
K = 8.99x10^9 Nm^2/C^2
F2on1 = F1on2 = k|q1||q2|/r^2

Question 21

Electrical force vs Gravitational force?

Answer 21

Electrical force is much stronger than gravitational force, which only has a G=10^-10 & K=10^+10
Fgravity = Gm1m2/r^2 = Felectric = K|q1||q2|/r^2

Question 22

Vector Addition of Electric Forces?

Answer 22

The net force exerted on particle j is?
Fnetonj = F1onj + F2onj + F3onj…..
- Add vectors up by breaking them up into their components

Question 23

what Is an Electric Field?

Answer 23

• The electric field at a point in space tells you how much force +1C charge would feel if it were placed at that point
• The electric field gives the force per unit charge
• The electric field is a vector quantity
• SI units of electric field are Newtons/Coulomb (N/C)

E = F/q = K|q|/r^2

Question 24

what is the direction of an electric field?

Answer 24

The direction of the field is radially outward from a positive charge, or radially inwards towards a negative charge

Question 25

What is the direction of an electric field between charged plates?

Answer 25

- The electric field points from the positive to the negative plate - the field is uniform E = Q/E0*A

Question 26

what is an electric field like mea a continuous charge distribution?

Answer 26

- divide the total charge (Q) into (n) mini-segments with charge (ΔQ) - treat each mini-segment as a point charge, and find the field due to each mini-segment - add the fields due to each mini-segment, component by component - The same becomes an integral as n->∞

Question 27

what are electric field lines?

Answer 27

A convenient aid for visualizing electric field patters is to draw lines pointing in the direction of the field vector at any point - the electric field is tangent to the electric field lines at each point

Question 28

what are the electric field line patterns?

Answer 28

1. for a positive source charge, the lines radiate outward | 2. for a negative source charge, the lines point inward

Question 29

The high density of lines means what?

Answer 29

The high density of lines between the two charges indicates the strong electric field in this region

Question 30

What is an electrocardiogram?

Answer 30

an electrocardiogram measures the changing field of the heart as it beats

Question 31

Motion of charged particles in an electric field?

Answer 31

- If a particle has a mass (m) and a charge (q) is placed in an electric field, it will feel a force F = qE therefore a = F/m = qE/m - If E is uniform then the particles acceleration is constant. in this case our KINEMATICS FORMULA apply