Magnetism and Electric Fields Flashcards
magnetic fields
vector quantities that represent the magnetic influence on an electrical charge of other moving charges or magnetized components
Sources of magnetic fields
electromagnetic radiation, permanent magnets, electrical current
magnetic fields from MRI come from
sequential conductive coil of current flowing in a circular direction
Capacitance
ability to store electric charge at small distances from one another, generates voltage
does not generate magnetic field
C=Q/V (farads)
charged particles
generate an electric field that exerts force on other surrounding charged particles
Lorentz force
exerts a moving charge in the presence of a magnetic field that is perpendicular to a particle’s velocity
trajectory is forced into a curved path with negative and positive charges bent in opposite directions
dielectrics
polarizable materials in which electric dipoles can be induced
decreases electric field and voltage, increasing capacitance
K = dielectric constant
capacitance equation
C=Q/V (farads)
charge/voltage
Electrostatic forces
known as Coulomb forces
it is the attractive or repulsive forces between two electrically charged objects
when charges are unbalanced, they become unstable
Coulomb’s Law equation
F = Kq1q2/r^2
k = 8.99 x 10^9 Nm^2/C^2
Insulators
keep charge to one location and do not transfer charges
electrons do not flow freely; very little electric current
Conductors
evenly space out charges within the system
transfer and transport charges
used in circuits and electrochemical cells
ex: metals and ionic solutions
Electric Fields
exert forces on other charges that move into the space of the field
E = kQ/r^2=Fe/q
E = ΔV/d
dividing coulomb’s law by “q”
Electric Potential Energy
U = kq1q2/r
like charges will cause a positive potential energy; with objects becoming more stable the further apart they are
opposite charges will have a negative potential energy; with objects becoming more stable the closer they are
Electric Potential energy definition
how much energy you need to move a charge against an electric field
ex: when I try to push the positive part of magnets together I have to put in a lot of energy to get them close to one another
magnetic force
Fb = qvBsinθ
charges must have a perpendicular component of velocity in order to experience a magnetic force
What happens if a charge is moving parallel to the magnetic field vector?
No magnetic force will be experienced. Magnetic forces only work when there is a perpendicular component of velocity
What is the charge of a proton?
1.6 x 10^-19C
centripetal force equation
mv^2/r
What is the speed of light?
c = 3 x 10^8 m/s
λf=c
equation for energy of a photon
E = f x h
h = plank's constant = 4 x 10^-15 eV*s h = 6.626 x 10^-34 kg m^2/s
E = ch/λ
electrical fields move?
transverse, perpendicular to each other
where is static electricity more significant?
in drier air because lower humidity makes it easier for charge to become and remain separated
coulomb unit
1.6 x 10^-19 C = e
1 C = 6.24 x 10^18 e
amount of energy each proton and electron have
Electric potential equation
V = kQ/r
when Q is positive, V is positive
when Q is negative, V is negative
Electric potential voltage equation
ΔV = Vb-Va = W/q
change in electric potential is the work it takes to bring object from infinity to point in electric field/magnitude to charge
when there is low potential energy because close to the oppositely charged plate, will have low electric potential. (opposite case when same charge)
W = negative when decrease in electric potential energy W = positive when increase in electric potential energy
How will a negative test charge move spontaneously through electric field?
move from lower electric potential to higher electric potential
positive test charge will move spontaneously move in direction that decreases their electric potential
what sign would W be if moving positive q from high to low electric potential?
W would be negative because moving with the electric fields does not require additional energy from Work and therefore would be a decrease is potential energy
What sign would W be if moving positive q from low to high electric potential?
W would be positive because work is required to move something against the concentration gradient. This would be an increase in potential energy
What is a high electric potential for a positive q
moving closer to another positive q would result in high electric potential because highly repulsive
electric dipole
2 equal and opposite charges being separated a distance d
can be transient like london dispersion forces or permanent like water and carbonyl groups
electric dipole moment equation
P = qd
C*m units
net torque on dipole equation
T = pE sin Θ
T = torque p= dipole moment e = magnitude of uniform external electric field
diamagnetic
atoms with no unpaired electrons
no net magnetic field
slightly repelled by magnet
includes things you don’t expect will get stuck to magnet: water, glass, plastic, skin, and wood
paramagnetic
atoms with unpaired electrons
has a net magnetic field
weakly magnetized in presence of external magnetic field
aluminum, copper, and gold
ferromagnetic
unpaired electrons
permanent atomic magnetic dipole
strongly magnetized when exposed to magnetic field
iron, nickel, and cobalt
bar magnets are ferromagnetic with north and south pole
magnetic field equation
B = μI/2πr
μ=permeability of free space (4π x 10^7 T*m/A)
I = current
for a circular loop, don’t need pi
magnetic field equation for straight wire
Fb = ILBsinΘ
I = current L = length B = magnetic field
How are J, C, and V related?
1 J = C * V
1 V = J/C
1C = J/V
Law of conservation of charge
net charge of an isolated system remains constant
ex: when ions are added to a neutrally charged solvent like water, the overall solution remains the same
How can you change the net charge of a system?
Introduce a charge from elsewhere or remove a charge from the system
electrostatic induction
charged object induces the movement/redistribution of charges in another object
something positive will cause all the positive charge to move away and the negative charge to move closer.
ex: like how a balloon sticks in your hair after you rubbed it on the carpet
electric potential
voltage
difference in potential energy per unit charge between two locations in an electric field.
units of magnetism
N s / C m = 1 Tesla = 10^4 Gauss
charge of electron/proton
1.6 x 10^19 C
mass of proton
1.6 x 10^-27 kg
mass of electron
9 x 10^-31 kg
electrospinning
when electric forces (generated by voltage source) at the surface overcome the surface tension and cause electrically charged jet to be ejected
dielectric constant
K
ability of a dielectric to increase the capacitance of a parallel plate relative to capacitance of a vacuum
C= K * C0
capacitance with dielectric = dielectric constant x initial capacitance
