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# EK Physics 7

### electricity and magnetism

units of charge coulombs (C)
universal law of conservation of charge the universe has no net charge, net charge is created by separating electrons from protons
Coulomb's law F = k*q1*q2/r^2 formula describing magnitude of the force of repulsion or attraction btw two charged objects
electric field lines always go... from positive to negative
the closer electric field lines are... the stronger the electric field
units to describe electric field N/C or V/m
electric field created by point charge formula E = k*q1/r^2
Force on charge q in an electric field F = Eq
potential energy of charge in an electric field U = Eqd
electric potential energy from coulomb's law U = k*q1*q2/r
what is the electric potential for particles separated by an infinite distance? zero
voltage potential for work by an electric field in moving any charge from 1 pt to another = Ed
units for voltage volts = J/C
voltage due to a point charge V = k*q1/r
what is a good conductor? allows e's to flow relatively freely, ex: metals
what is a poor conductor/good resistor? hold e's tightly in place, ex: network solids like diamond and glass
induction process to charge a conductor
current moving charge, given in amps (A = C/s), its flow is in the direction of positive charge
circuit cyclical pathway for moving charge
resistivity quantitative measure of how much substance resists flow of charge
resistance (R) is the quantitative measure of an object of articular shape and size to resist flow, measured in ohms; depends on resistivity, length of wire and cross sectional area of wire
voltage relates to current and resistance by V = iR (ohm's law)
the amount of current flowing into any node must be ____ the same that flows out.
the voltage around any path in a circuit must sum to ____ zero
electromotive force EMF, rates the batteries, analogous to voltage
capacitor used to temporarily store energy in a circuit
parallel plate capacitor two plates made from conductive material separated by small distance where 1 plate holds positive charge and the other holds exact same amt of neg charge
electric field in capacitor E = (1/K)*(Q/A*eo) where K is dielectric constant, Q is charge on either plate, A is the area of the plate, and eo is derived from Coulomb's constant
capacitance ability to store charge per unit voltage C = Q/V
capacitance of parallel plate capacitor C= K(A*eo/d) where d is sep distance and A is the plate area *increased surface area increases C and increasing sep distance decreases C
energy stored in capacitor = U = 1/2*QV = 1/2*CV^2 = 1/2*QC^2
dielectric constant substance btw plates of capacitor, insulator material, acts to resist creation of electric field so ti can store more charge
resistors in series Reff = R1 + R2 + R3 +...
resistors in parallel 1/Reff = 1/R1 + 1/R2 + 1/R3 ..
capacitors in series 1/Ceff = 1/C1 + 1/C2 + 1/C3 ...
capacitors in parallel Ceff = C1 + C2 + C3 ...
electrical power P = iV = i^2*R = V^2/R
DC current direct current, where net movement of e's is in 1 direction around circuit
AC current alternating current, created by oscillating e's back and forth in SHM
Vmax in AC current =sqrt(2)*Vrms
imax in AC current =sqrt(2)*irms
magnetic field unit tesla, T
magnetic field lines go from.. north to south poles
magnetic field created by... CHANGING electric field
right hand rule for magnetic field - the palm is... force of charge moving thru magnetic field
right hand rule for magnetic field - the thumb is... velocity of charge moving thru magnetic field
right hand rule for magnetic field - the fingers are... direction of magnetic field
force of a charge moving thru magnetic field = F = qvBsin(theta) where theta is the angle btw magnetic field and velocity of charge
force is directed _____ to both the velocity and magnetic field perpendicularly
does magnetic force do work? no, the force is always perpendicular to velocity and magnetic field so cannot apply force in the direction of movement
force on a current carrying wire in a magnetic field = F = iLBsin(theta) where L is the length of the wire, and theta is the angle between wire and B
a changing magnetic field ___ creates an electric field, but this field is NON CONSERVATIVE--> loop of wire pulled out of magnetic field will develop current in wire
faraday's law describes how changing magnetic field induces emf = flux (magnetic field of over an area over time)
Lenz' law induced current will create a magnetic field opposing the inducing magnetic field
eddy currents result when a conductor is moved thru magnetic field - pendulum in a magnetic field will stop swinging from the resistivity and absorption of internal energy so KE changed to heat
Created by: miniangel918

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