electro

Question 1

insulator v conductor

Answer 1

electrons held close to nuclei vs not

insulators do not distribute charge over surface, conductors do

Question 2

Coulombs law

Answer 2

= magnitude of electrostatic force between two charges

Fe = k(q1q2)/ r^2

k = electrostatic constant
q1 q2= two charges
r = distance between charges

Question 3

Electric field

Answer 3

every electric sets up electric field around it

• make their presence known by exerting forces on other charges
• attract/repell force- determine through test charge
• vector quantity, has direction

Question 4

Find magnitude of electric field

Method #1

Answer 4

method 1: E= Fe/ q
electrostatic force divided by q

method 2: E = kQ / r^2
without test charge q

q = test charge 
Q = source of the force felt by the test charge 

electric field = vector so this is magnitude, how to find direction?
use R hand rule:

Question 5

Magnitude of electric field

Method #2

Answer 5

does not require test charge
need to know:
- magnitude of source charge Q
- distance between Q and some point in space at which we want to measure the E- field

method 2: E = kQ / r^2

Question 6

Electric field vector

Answer 6

direction that a positive test charge would move in the presence of a source charge

• would repel away from another +
• would come toward another -

positive charges have field vectors that radiate outward
negative charges have field vectors that radiate inward

field is stronger where field lines are closer together

Question 7

Electric Field vector and direction of e- force

Answer 7

in regards to e- field and direction of
electrostatic force:
- for a positive test charge q, the force is in the direction of the e- field
- for a negative test charge q, the force is in the direction opposite of the e- field

Question 8

Electric potential energy

Answer 8

4th form of potential energy

EPE= U = kQq / r
measured in joules

a positive EPE = charges are like, repel, loaded

a negative EPE= charges are opp, attract, will become increasingly negative as charges are brought closer
here increasingly negative–> decreasing value

EPE also = the amount of work necessary to being the charge from infinity to that point

Question 9

Electric potential energy as work

Answer 9

= the amount of work necessary to being the charge from infinity to that point

EPE= U = W = Fdcos (theta) = kQq/r
measured in Joules

Question 10

Electric potential

Answer 10

= ratio of the magnitude of the electric potential energy and the magnitude of the charge itself
its EPE over its charge

V = EPE/q = U/q
measured in volts, 1 volt = 1 J/C

is a scalar quantity, sign determined by Q:

• Q is + then V is +
• Q is - then V is -

Question 11

Find Electric potential without test charge

Answer 11

V = kQ/ r

Question 12

Voltage

Answer 12

since two different points at two different places will have different electric potentials,
they are said to have potential difference

voltage = potential difference 
voltage = deltaV = Vb - Va

Question 13

Voltage and work

Answer 13

voltage = deltaV = Vb- Va = Wab/q

where Wab is the work it would take to move a test charge q through an e- field from point a to point b

point a and b are not charges, just places

For a +q:
will move to decrease electric potential
moving from higher potential to lower potential is spont:
so if Va > Vb then deltaV will be negative
then work will be negative, represents decrease in EPE

For a -q:
will move to increase electric potential V
opposite is true, work is negative if Va < Vb
W (-) / q(-) = positive delta V
work is still negative so EPE still decrease

Question 14

equation chart

Answer 14

pg `161

Question 15

Equitpotent lines

Answer 15

Lines where potential is the same at any point along the line

ex: electron orbital, potential only varies when u jump to another orbital (work done, depends on the potential difference or voltage)

Question 16

Calculate the electric potential at some point P near the dipole

Answer 16

need picture

V= (kq/r1) - (kq/r2)

For points relatively distant from the dipole,

V = (kqd)/r^2 x cos theta
what is theta

Question 17

dipole moment

Answer 17

p=qd

Question 18

perpendicular bisector of the dipole

Answer 18

along this, electric potential = 0

Question 19

Magnetic field & types

Answer 19

created by any moving charge.
measured in Tesla

diamagnetic = atoms of no unpaired e-, no net mag field

• slightly repelled by magnetic, weakly anti-magnetic
• i.e.: wood, plastic, glass, skin

paramagnetic = have unpaired e-, become weakly magnetized and align dipoles in e- field presence

• but reorient randomly upon removal
• i.e.: aluminum, copper, gold

ferromagnetic = unpaired e-, strongly magnetized in mag field,

Question 20

Magnitude of magnetic field for linear wire

Answer 20

B = (uo)I / 2pi(r)
gives magnitude at any perpendicular distance r from the wire

I = current 
uo = permeability of free space constant

straight wires form mag field lines in concentric way:

to determine direction:
R hand rule, closed palm, fingers wrap:
thumb = current
wrapped fingers = magnetic field lines

Question 21

Magnitude of magnetic field for looped wire

Answer 21

B = (uo)I/2r
missing pi

gives magnitude only at center

to determine direction:
R hand rule, closed palm, fingers wrap:
thumb = current
wrapped fingers = magnetic field lines

Question 22

Force on moving charge

Answer 22

magnitude:

Fb = qvB sin theta

q= the charge 
B= mag of magnetic field
v= velocity 
theta = minimal angle bw B and v

to determine direction of force= 2nd R hand rule

• open palm = Fb, force direction
• thumb = velocity way
• fingers = field lines of B mag field

Question 23

Force on current carrying wire

Answer 23

Fb = ILB sin theta

theta is angle bw B and L
L = length of wire

Question 24

Lorentz force

Answer 24

Sum of electrostatic and magnetic forces on a body