Electrostatics and Magnetism Flashcards
what kind of force does electrostatic forces produce?
repulsive or attractive
ground
a means if returning charge to the earth
why is static charge buildup (static electricity) more significant in drier air?
lower humidity makes it easier for charge to become and remain separated
coulomb
the SI unit for charge;
e=1.60 x 10^-19 C, value for proton and electron
law of conservation of charge?
charge can neither be created nor destroyed
insulator
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
dielectric material
in electric fields, these materials do not allow electric charges to flow through them; insulators
conductor
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
coulomb’s law
quantifies the magnitude of electrostatic force between two charges
Fe= (kq1q2)/ r^2
Fe=electrostatic force
k=coulombs constant (electrostatic constant)
coulombs constant
1/(4pi(eo)) = 8.99 x 10^9 (NxM^2)/C^2
eo= permittivity of free space
electric field
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
what determines in an electric field if the force felt is attractive or repulsive?
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
what is the convention of electric field vectors?
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
field lines
imaginary lines that represent how a positive test charge would move in the presence of the source charge
electrical potential energy (U)
U=kQq/r
how does work and electrical potential energy relate?
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
electrical potential (V)
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
voltage
the potential difference between two electrical points a and b
deltaV=Vb-Va= Wab/q
Wab
the work needed to move a test charge q through an electric field from point a to point b
what is the direction that a positive test charge will move? what about a negative test charge?
- 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
equipotential line
a line on which the potential at every point is the same, in a 3D image, the lines create a sphere around the source
electrical potential near a dipole
V=(kqd)cos/ r^2
dipole moment (p)
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
perpendicular bisector of the dipole
any point that lies along the plane that is halfway between +q and -q (perpendicular to these) will have an electrical potential of zero
electric field on the perpendicular bisector of a dipole
E=1/(4pi(eo))xp/r^3
or
E=kp/r^3
p=dipole moment (point in direction according to physics, negative to positive)
net torque on a dipole
t=pEsin(theta)
p=dipole moment
E=magnitude of the external electrical field
theta=the angle the dipole moment makes with the electric field
magnetic fields
created by magnets and moving charges; unit is tesla (T)= Ns/mC and 1 T= 10^4 gauss
diamagnetic
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
paramagnetic
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
ferromagnetic
have unpaired electrons; will become strongly magnetic in an external magnetic field or under certain temps
magnetic field from a straight wire
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
magnetic field from a loop of wire
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
which way do the field lines point in magnets?
field lines point from the north to the south pole
Lorentz Force
the sum of electrostatic and magnetic forces
magnetic force on a moving point charge
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
magnetic force on a current carrying wire
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)
