Electrostatics and Magnetism

Question 1

What is the purpose of Coulomb’s law? What is the equation? What does the direction depend on?

Answer 1

Calculate the magnitude of the electrostatic force between 2 charges:
Fe = k . q1 . q2 / r^2
Direction: depends on whether the force is attractive or repulsive

Question 2

What are the 2 equations to calculate the magnitude of an electric field? Unit?

Answer 2

E = Fe / q = k.Q/r^2
Q: source charge magnitude
q: test charge
N/C

Question 3

What direction does a negative electrostatic force point?

Answer 3

Toward the point

Question 4

What direction does a positive electrostatic force point?

Answer 4

Away from the point

Question 5

What is the purpose of calculating the electrical potential energy? What does it represent? What is the equation?

Answer 5

To calculate the potential E that is dependent upon the relative position of one charge with respect to another
It is the work necessary to move a test charge from infinity to a point in space in an electric field surrounding a test charge

U = k.Q.q/r = Delta V . q

Question 6

What does a negative electrical potential energy mean?

Answer 6

Opposite charges

Question 7

What does a positive electrical potential energy mean?

Answer 7

Like charges

Question 8

How is electrical potential energy related to the stability of the system?

Answer 8

Negative U: as U decreases, it becomes more stable (=as the charges get closer)
Positive U: as U decreases it becomes more stable (=as the charges get further from each other)

Question 9

What is the equation for electrical potential?

Answer 9

V = U / q = k. Q/r

Question 10

What are volts?

Answer 10

J/C

Question 11

What is the potential difference equation? What is it equal to?

Answer 11

Delta V = Vb - Va = Wab/q

= voltage

Question 12

What is an equipotential line?

Answer 12

Line on which the U at every point is the same: Delta U = 0

Question 13

How can a charge move from one equipotential line to the other?

Answer 13

Work is done and is independent of the path taken

Question 14

How to calculate the electrical potential of a charge that is far from a dipole?

Answer 14

V = kqd/r^2 x cos theta = k.p/r^2 x cos theta

p = dipole moment

Question 15

What is the dipole moment equation? Unit?

Answer 15

p = q.d
Unit: C.m
Sometimes debye: 1 D = 3.34 x 10^-30 C.m

Question 16

What is a Tesla equal to? What is it used for?

Answer 16

1 T = 1 N.s/m.C

Magnetic fields

Question 17

How to calculate the magnitude of the electric field on the perpendicular bisector of a dipole?

Answer 17

E = p / 4.pi.Eo.r^3

Question 18

How to calculate the net torque on a dipole?

Answer 18

t = p.E.sin theta
Theta = angle between dipole and electric field

Question 19

What is a paramagnetic material?

Answer 19

it has unpaired electrons with unbalanced spin –> will become WEAKLY magnetic in an external magnetic field

Question 20

What is a diamagnetic material?

Answer 20

Diamagnetic materials don’t have electrons with uncanceled spins –> will be slightly repelled by a magnet

Question 21

What is an exception to the electron rule of para/diamagnetic materials?

Answer 21

O2 is paramagnetic

Question 22

What is a ferromagnetic material?

Answer 22

Possesses some unpaired electrons and become STRONGLY magnetic in an external magnetic field

Question 23

What are some examples of paramagnetic materials?

Answer 23

Al, Cu, gold

Question 24

What are some examples of diamagnetic materials?

Answer 24

wood, plastic, glass

Question 25

What are some examples of ferromagnetic materials?

Answer 25

Ir, Ni, Cb

Question 26

How to calculate the magnitude of the magnetic field produced by a current in an infinitely long wire?

Answer 26

B = permeability of free space . I / 2.pi.r

Question 27

How to calculate the magnitude of the magnetic field produced by a current in a circular wire?

Answer 27

B = permeability of free space . I / 2.r

Question 28

What is a gauss?

Answer 28

1 Tesla = 10^4 gauss

Question 29

How to remember the F, U, V, E equations in this chapter?

Answer 29

From left to right: multiply by r | From top to bottom: divide by q

Question 30

How to calculate the potential energy in terms of the work?

Answer 30

Delta U = W = F . d. cos theta

Question 31

What is the effect on electrical potential energy when two opposite charges move apart?

Answer 31

Increase

Question 32

What is the effect on electrical potential energy when two opposite charges move toward each other?

Answer 32

Decrease

Question 33

What is the effect on electrical potential energy when two like charges move apart?

Answer 33

Decrease

Question 34

What is the effect on electrical potential energy when two like charges move toward each other?

Answer 34

Increase

Question 35

How to calculate the magnetic force on a moving charge?

Answer 35

Fb = q. v. B. sin theta Theta: smallest angle between v and B

Question 36

What happens if a charge moves parallel to a magnetic field?

Answer 36

It will not experience a force

Question 37

How to calculate the magnetic force on a current carrying wire?

Answer 37

Fb = I.L.B. sin theta L = length of wire Theta: angle between L and B

Question 38

To create an electric field, one needs a...?

Answer 38

Charge

Question 39

To create a magnetic field, one needs a...?

Answer 39

Moving charge

Question 40

To create a magnetic force, one needs a...?

Answer 40

External electric field acting on a charge moving in any direction BUT parallel or antiparallel to the electric field

Question 41

What is the right hand rule?

Answer 41

1. Place your thumb in the direction of the current or velocity 2. Position your fingers either going in or out of the page depending on the question stem 3. Your palm is facing the direction in which the magnetic force acts on a + charge 4. The back of your hand is facing the direction in which the magnetic field acts on a - charge

Question 42

What is the Lorentz force?

Answer 42

The sum of the electrostatic and magnetic forces acting on a body

Question 43

How are the change in potential energy and the change in potential related?

Answer 43

W = Delta U = q.Delta V

Question 44

What is lost potential energy converted to?

Answer 44

Kinetic energy

Question 45

How do you calculate the word to place 3 charges next to each other?

Answer 45

1. The work to place the first charge is 0 2. The work to place the second charge is: W=k.Q.q/r^2 3. The work to place the third charge is: W = k.q. (Q1/r1 + Q2/r2) 4. Add all of them together

Question 46

How do you calculate the amount of work required to change the distance between 2 charges?

Answer 46

W = Delta U = k.Q.q. (1/r1 - 1/r2)

Question 47

Can a magnetic field act on a static charge?

Answer 47

No

Question 48

What is the difference between an electric and a magnetic field?

Answer 48

Charges only experience a magnetic field if they are moving