Electrostatics and Magnetism Flashcards
What is the purpose of Coulomb’s law? What is the equation? What does the direction depend on?
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
What are the 2 equations to calculate the magnitude of an electric field? Unit?
E = Fe / q = k.Q/r^2
Q: source charge magnitude
q: test charge
N/C
What direction does a negative electrostatic force point?
Toward the point
What direction does a positive electrostatic force point?
Away from the point
What is the purpose of calculating the electrical potential energy? What does it represent? What is the equation?
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
What does a negative electrical potential energy mean?
Opposite charges
What does a positive electrical potential energy mean?
Like charges
How is electrical potential energy related to the stability of the system?
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)
What is the equation for electrical potential?
V = U / q = k. Q/r
What are volts?
J/C
What is the potential difference equation? What is it equal to?
Delta V = Vb - Va = Wab/q
= voltage
What is an equipotential line?
Line on which the U at every point is the same: Delta U = 0
How can a charge move from one equipotential line to the other?
Work is done and is independent of the path taken
How to calculate the electrical potential of a charge that is far from a dipole?
V = kqd/r^2 x cos theta = k.p/r^2 x cos theta
p = dipole moment
What is the dipole moment equation? Unit?
p = q.d
Unit: C.m
Sometimes debye: 1 D = 3.34 x 10^-30 C.m
What is a Tesla equal to? What is it used for?
1 T = 1 N.s/m.C
Magnetic fields
How to calculate the magnitude of the electric field on the perpendicular bisector of a dipole?
E = p / 4.pi.Eo.r^3
How to calculate the net torque on a dipole?
t = p.E.sin theta Theta = angle between dipole and electric field
What is a paramagnetic material?
it has unpaired electrons with unbalanced spin –> will become WEAKLY magnetic in an external magnetic field
What is a diamagnetic material?
Diamagnetic materials don’t have electrons with uncanceled spins –> will be slightly repelled by a magnet
What is an exception to the electron rule of para/diamagnetic materials?
O2 is paramagnetic
What is a ferromagnetic material?
Possesses some unpaired electrons and become STRONGLY magnetic in an external magnetic field
What are some examples of paramagnetic materials?
Al, Cu, gold
What are some examples of diamagnetic materials?
wood, plastic, glass
What are some examples of ferromagnetic materials?
Ir, Ni, Cb
How to calculate the magnitude of the magnetic field produced by a current in an infinitely long wire?
B = permeability of free space . I / 2.pi.r
How to calculate the magnitude of the magnetic field produced by a current in a circular wire?
B = permeability of free space . I / 2.r
What is a gauss?
1 Tesla = 10^4 gauss
How to remember the F, U, V, E equations in this chapter?
From left to right: multiply by r
From top to bottom: divide by q
How to calculate the potential energy in terms of the work?
Delta U = W = F . d. cos theta
What is the effect on electrical potential energy when two opposite charges move apart?
Increase
What is the effect on electrical potential energy when two opposite charges move toward each other?
Decrease
What is the effect on electrical potential energy when two like charges move apart?
Decrease
What is the effect on electrical potential energy when two like charges move toward each other?
Increase
How to calculate the magnetic force on a moving charge?
Fb = q. v. B. sin theta
Theta: smallest angle between v and B
What happens if a charge moves parallel to a magnetic field?
It will not experience a force
How to calculate the magnetic force on a current carrying wire?
Fb = I.L.B. sin theta
L = length of wire
Theta: angle between L and B
To create an electric field, one needs a…?
Charge
To create a magnetic field, one needs a…?
Moving charge
To create a magnetic force, one needs a…?
External electric field acting on a charge moving in any direction BUT parallel or antiparallel to the electric field
What is the right hand rule?
- Place your thumb in the direction of the current or velocity
- Position your fingers either going in or out of the page depending on the question stem
- Your palm is facing the direction in which the magnetic force acts on a + charge
- The back of your hand is facing the direction in which the magnetic field acts on a - charge
What is the Lorentz force?
The sum of the electrostatic and magnetic forces acting on a body
How are the change in potential energy and the change in potential related?
W = Delta U = q.Delta V
What is lost potential energy converted to?
Kinetic energy
How do you calculate the word to place 3 charges next to each other?
- The work to place the first charge is 0
- The work to place the second charge is: W=k.Q.q/r^2
- The work to place the third charge is: W = k.q. (Q1/r1 + Q2/r2)
- Add all of them together
How do you calculate the amount of work required to change the distance between 2 charges?
W = Delta U = k.Q.q. (1/r1 - 1/r2)
Can a magnetic field act on a static charge?
No
What is the difference between an electric and a magnetic field?
Charges only experience a magnetic field if they are moving
