Electrostatics and Magnetism

Question 1

what kind of force does electrostatic forces produce?

Answer 1

repulsive or attractive

Question 2

ground

Answer 2

a means if returning charge to the earth

Question 3

why is static charge buildup (static electricity) more significant in drier air?

Answer 3

lower humidity makes it easier for charge to become and remain separated

Question 4

coulomb

Answer 4

the SI unit for charge;

e=1.60 x 10^-19 C, value for proton and electron

Question 5

law of conservation of charge?

Answer 5

charge can neither be created nor destroyed

Question 6

insulator

Answer 6

will not easily distribute a charge over its surface and will not transfer that charge to another neutral object very well; tend to be nonmetals

Question 7

dielectric material

Answer 7

in electric fields, these materials do not allow electric charges to flow through them; insulators

Question 8

conductor

Answer 8

when given a charge, these will distribute approximately evenly upon the surface if the conductor, able to transfer and transport charges. usually material with more free electrons; metals

Question 9

coulomb’s law

Answer 9

quantifies the magnitude of electrostatic force between two charges
Fe= (kq1q2)/ r^2

Fe=electrostatic force
k=coulombs constant (electrostatic constant)

Question 10

coulombs constant

Answer 10

1/(4pi(eo)) = 8.99 x 10^9 (NxM^2)/C^2

eo= permittivity of free space

Question 11

electric field

Answer 11

make their presence known by exerting forces on other charges that move into the space of the field; a vector quantity

E=Fe/q=kQ/r^2

Question 12

what determines in an electric field if the force felt is attractive or repulsive?

Answer 12

it depends on whether the stationary test charge (q=the charge placed in the electric field) and the source charge (Q=what creates the electric field) are opposite charges or like charges

Question 13

what is the convention of electric field vectors?

Answer 13

the direction of the force in an electric field is given as the direction a positive test charge would move in presence of the source charge. So a source of positive charge gives repulsive forces while a negative source charge gives attractive forces

Question 14

field lines

Answer 14

imaginary lines that represent how a positive test charge would move in the presence of the source charge

Question 15

electrical potential energy (U)

Answer 15

U=kQq/r

Question 16

how does work and electrical potential energy relate?

Answer 16

we can define electrical potential energy for a charge at a point in space in an electric field as the amount of work necessary to bring the charge from infinitely far away to that point

Question 17

electrical potential (V)

Answer 17

not the same a U and is a scalar quantity, sign is determined by the source charge Q. the work necessary to move a test charge from infinity to a point in space in an electric field surrounding a source charge

V= U/q or V=kQ/r (when not test charge present)

units: volts (V)= 1 J/C

Question 18

voltage

Answer 18

the potential difference between two electrical points a and b

deltaV=Vb-Va= Wab/q

Question 19

Wab

Answer 19

the work needed to move a test charge q through an electric field from point a to point b

Question 20

what is the direction that a positive test charge will move? what about a negative test charge?

Answer 20

• a positive test charge will move from position of higher electrical potential to a position of lower electrical potential= voltage will be negative here
• a negative test charge will spontaneously move form a position of lower electrical potential to a position of higher electrical potential=voltage will be positive here

Question 21

equipotential line

Answer 21

a line on which the potential at every point is the same, in a 3D image, the lines create a sphere around the source

Question 22

electrical potential near a dipole

Answer 22

V=(kqd)cos/ r^2

Question 23

dipole moment (p)

Answer 23

the product of charge and separation distance; a vector. In chem the dipole points from positive to negative while physics has dipole point from negative to positive
SI unit: Cxm

p=qd

Question 24

perpendicular bisector of the dipole

Answer 24

any point that lies along the plane that is halfway between +q and -q (perpendicular to these) will have an electrical potential of zero

Question 25

electric field on the perpendicular bisector of a dipole

Answer 25

E=1/(4pi(eo))xp/r^3
or
E=kp/r^3

p=dipole moment (point in direction according to physics, negative to positive)

Question 26

net torque on a dipole

Answer 26

t=pEsin(theta)

p=dipole moment
E=magnitude of the external electrical field
theta=the angle the dipole moment makes with the electric field

Question 27

magnetic fields

Answer 27

created by magnets and moving charges; unit is tesla (T)= Ns/mC and 1 T= 10^4 gauss

Question 28

diamagnetic

Answer 28

materials made of atoms with no unpaired electrons and that have no net magnetic field, slightly repelled by a magnet and so can be called weakly antimagnetic

Question 29

paramagnetic

Answer 29

have unpaired electrons, become weakly magnetized in the presence of an external magnetic field aligning the magnetic dipoles of the material with the external field

Question 30

ferromagnetic

Answer 30

have unpaired electrons; will become strongly magnetic in an external magnetic field or under certain temps

Question 31

magnetic field from a straight wire

Answer 31

B= (uo)I/(2pir)

B=magnetic field at a distance r from the wire
uo=permeability of free space (4pix10^-7 Tm/A)
I=current

Question 32

magnetic field from a loop of wire

Answer 32

B= (uo)I/(2r)

B=magnetic field at a distance r from the wire
uo=permeability of free space (4pix10^-7 Tm/A)
I=current

Question 33

which way do the field lines point in magnets?

Answer 33

field lines point from the north to the south pole

Question 34

Lorentz Force

Answer 34

the sum of electrostatic and magnetic forces

Question 35

magnetic force on a moving point charge

Answer 35

Fb=qvBsin(theta)

Fb=magnetic force
q=charge
v=velocity 
B=magnitude of the magnetic field
theta= smallest angle between the velocity vector v and the magnetic field vector B

Question 36

magnetic force on a current carrying wire

Answer 36

Fb=ILBsin(theta)

Fb=magnetic force 
I=current 
L=length of the wire
B=magnitude of the magnetic field 
theta= angle between L and B

in the right hand rule, current is considered the flow of positive charge (v)