2 - Forces & Fields

Question 1

What Is An Insulator?

Answer 1

When electrons are tightly bound and not free to move within the valence shell of the substance.

Question 2

What Is A Conductor?

Answer 2

Electrons are able to move about of the outermost (valence) shell.

Question 3

What Is A Semi Conductor?

Answer 3

Materials that lie between good conductors and good insulators.

They are good conductors in certain situations, and good insulators in other situations.

EX… Selenium is a good insulators in the dark, but a good conductor in the presence of light. (this makes it useful in photocopiers)

Question 4

What Is A Super Conductor?

Answer 4

Conductive at very low temperatures.

EX… Solid mercury lost its electrical resistance when cooked to a temperature of -269°C.

Scientists have a goal to develop superconductors that operate at room temperature.

Question 5

What Is The Law Of Conservation Of Charge?

Answer 5

The net charge of an isolated system is conserved.

Net charge is the sum of all electrical charge in the system.
EX… if a system contains + 3 C of a charge and - 5 C of a charge, the net charge is - 2

New charges have not been created, only rearranged.

Question 6

Explain What Happens When You Charge An Object By Rubbing Or Friction.

Answer 6

This method separates electrons from the atoms in one object through rubbing it and then transferring and depositing these electrons (now possessing positively charged ions) to the atoms of another object (now possessing negatively charged ions).

Question 7

What Is Conduction?

Answer 7

Process of charging an object through the contact of another object where electrons are transferred to distribute charge.

EX…
4.0μC ◯ —-> ◯
__________________________________________
2.0μC ◯◯ 2.0μC

☆An object with a bigger surface area gets more charge then a smaller object

Question 8

What Happens To The Charges After it Has Transferred To…

a) A Conductor
b) An Insulator

Answer 8

a) With a conductor, it will distribute over the surface of the object
b) With an insulator, it will remain on the surface at the point of contact.

Question 9

Explain What Happens When You Charge Objects By Induction.

Answer 9

Charges in a neutral object shift or migrate because of the presence of an external charged object. This temporary charge separation polarizes the neutral object. On side becomes negatively charged while the other side becomes equally positively charged. The object then acts as if were charged but it is still neutral.

☆They do not touch so there isn’t an actual transfer of charge

Question 10

What Is Induction?

Answer 10

MOVEMENT of electrons by an external charged objects.

Question 11

What Is Charge Migration / Polarization?

Answer 11

Movement of electrons in a neutral object where one side become negative and the other becomes positive..

Question 12

What Is A Charge Shift?

Answer 12

Movement of electrons in an ATOM where one side of the atom becomes positive and the other side becomes negative.

Question 13

What Is Grounding?

Answer 13

The process of transferring electrons to and from the Earth.

Question 14

What Are The Four Steps To Charging AN Object By Induction?

Answer 14

1) A charged object causes polarization of the object to be charged (no touching)
2) Ground the object to be charged
3) “Remove” the ground
4) Removed the charged object

☆The object to be charged will ALWAYS be OPPOSITE to the charged object

EX…

(Positively Charged) (neutral / grounded)
◯ ◍———GROUND
_________________________________________
◯◍–(e- travelling to the pith ball)—-GROUND
_________________________________________
◯ ⚫ (disconnected from ground/ negatively charged)

Question 15

What Is Coulombs Law?

Answer 15

F e = (kq₁q₂) / (r²)

F e is electrostatic force (N)
q₁ is the charge on object 1 (C)
q₂ is the charge on object 2 (C)
r is the separation distance between the centers (m)
k is Coulombs constant (8.99x109(Nm2/C2))☆☆☆☆☆

This electrostatic force is attractive if the two objects have opposite charges and repulsive if the two objects have the same charge.

Question 16

What Is A Field?

Answer 16

A region of influence surrounding an object.

Question 17

What Is An Electric Field?

Answer 17

Region of influence surrounding an object that has both magnitude and direction. (It is a vector field)

The field has an arrow, the length can vary, to represent the magnitude of the electric field.

Question 18

What Is A Test Charge?

Answer 18

A charge with a magnitude small enough so that it doesn’t disturb the charge on the source charge and thus change its electrical field.

The closer a test charge is to the source charge, the greater the electrical field strength.

☆Test charges are always positive.

Question 19

What Equation is used To Determine The Electric Field?

Answer 19

E = Fe / q₂

E is the electric field (N / C) or (V / m)
Fe is he electrostatic force (N)
q₂ is the charge on the test charge (C)

This equation attempts ti explain the interaction of charged

☆Equations based on Coulombs’ law only work for point charges.

Question 20

What Equation Is Used To Determine The MAGNITUDE Of The Electric Field?

Answer 20

E = kq₁ / r²

E is the electric field (N / C)
k is Coulombs constant
q₁ is the charge on the source charge (C)
r is the separation distance between the centers (m)

This equation is used to calculate the electric field from a point charge.

☆Equations based on Coulombs’ law only work for point charges.

Question 21

What Way Do Electric Field Lines Go With A…

a) Positive Source Charge?
b) Negative Source Charge?

Answer 21

a) With a positive source charge, electric field lines point AWAY from the charge to infinity.
b) With a negative source charge, electric field lines point INTO the charge and terminate at the negative source charge.

☆The more closely spaced and the greater the number of lines, the stronger the electric field.

☆To determine the direction of the electric field lines, imagine there being a positive test charge near it.

Question 22

What Happens With Charges In A Solid Conducting Sphere? (Either Positively Or Negatively Charged)

Answer 22

All charges move as far apart as possible because of the electrostatic forces of repulsion.

Question 23

What happens With Charges On A Solid, Flat, Conducting Plate? (Either Positively Or Negatively Charged)

Answer 23

Excess charges, either positive or negative, on a solid, flat, conducting plate spread out and distribute evenly along the outer surface of a charged plate due to repulsion.

Question 24

What happens With Charges On A Irregularly Shaped Solid Conducting Object?

(Like the top of the arch of the “m” for McDonald’s)

Answer 24

The charges don’t really distribute evenly on the outer surface. The charges are more dense where the surface curves the sharpest (top of the arch of the “m”) and the electrical field lines at this point are also more dense.

Question 25

What happens With Charges On A Hollow Conducting Object?

Answer 25

They move as far apart as possible because of electrostatic forces of repulsion.

They only distribute on the outer surface of the conducting object. There is no excess charge on the inner surface of the hollow object, no matter what the shape of the object is.

☆The electric field strength inside the hollow, conducting object is zero. (There is no electrical field lines inside)

Question 26

What Happens With Charges On Parallel Plates? (The Two Metal Plates Are Oppositely Charged)

Answer 26

The distribute evenly within each plate, and electrostatic forces of attraction of opposite charges on the two plates cause charges to accumulate on the inner surfaces.

They also distribute evenly across the inner surface of the charged plates.

Question 27

Why Do Parallel Plates Have Uniform Fields While Charged Objects (Like A Ball Or A Planet) Have Non-Uniform Fields?

Answer 27

Parallel plates are distributed evenly and where ever you place a test charge, the E (electric field) will be the same, making the field uniform.

With a planet, the closer a moon is, the greater the field. The farther away it is, the weaker the field. This makes it non-uniform.

Question 28

What Is Similar Between Gravitational Potential Energy And Electric Potential Energy?

Answer 28

Gravitational potential energy is is the energy stored in an object due to its vertical position above the earth.

When putting work into an object and moving it up (against nature / gravity) it results in an increase in Ep. When no work is applied, the object is forced down by gravity and results in a loss in Ep.

EX… If the same object is moved from point A to a higher point, B, it will have more potential energy at point B. If a mass of m is at a height of 2h, it could have the same Ep as an object with a mass of 2m and a height of h.

Gravitational potential energy = △Ep = W = mgh

Electric potential energy is similar because the charge is like the mass and the distance away from the source charge is like the height from the ground.

With a positive source and test charge, work is put into the test charge to move it towards the source charge which allows an increase in electric potential energy.

Electric potential energy = J = △Ep

W = Fd = mad = △E = Vq

☆ twice the charge (or) twice the mass = twice the work

Question 29

What Is Similar Between Gravitational Potential And Electric Potential.

Answer 29

Gravitational potential is the potential energy per kilogram. No matter the mass of the object, the same height will have the same gravitational potential.

EX… Object A has a mass of m and object B has a mass of 2m. If they are places at a height of h, they will have the same gravitational potential. If they are both placed at a height of 2h, they will have an equal but greater gravitation potential.

Gravitational potential = Ep / m = J / kg

Electric potential is the potential energy per charge.

No matter the charge, it will have the same electric potential at the same separation distance.

Electric potential = Volts = △V = Ep/q

W = Fd = mad = △E = Vq

Question 30

Suppose The Magnitude Of A Charge Placed In A Uniform Electric Field Were Doubled. How Much Would The….

a) Electric Potential Energy Change?
b) Electric Potential Change?

Answer 30

a) the electric potential energy would double as it is a direct relationship.
b) the electric potential would stay the same because it would still be in the same location.

Question 31

When Work Is Done On A Positive Test Charge By An External Force To Move It From One Location To Another, Potential Energy (Increases Or Decreases) And The Electric Potential ( Increases Or Decreases)

Answer 31

The potential energy increases and the electric potential increases.

Question 32

A Battery Can Charge Parallel Plates.

Answer 32

___________(+ plate)━━
│
↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ━ (Positive side of battery
(electric field) - (Negative side of battery)
│
___________(- plate) ━━