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94 Cards in this Set
- Front
- Back
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Electric charge is
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a fundamental property of matter: it comes in invariant quantized amounts of size +-e
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The absolute value of the smallest nonzero physical amount of electric charge is:
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e or 1.602x10^-19
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It is usually approximately electrically neutral
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what is ordinary, terrestrial matter above the atomic scale
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Why don't positive and negative charge necessarily neutralize each other at the microscopic level just like they mostly do at the macroscopic level? It is forbidden by __________,
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Quantum Mechanics
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Ordinary matter is positively charged whenever protons
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outnumber electrons.
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Electrons in an atom are
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not permanently bound to the atom
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Which of electrons, protons, neutrons are easier to remove from an atom?
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Electrons
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Given the mass of a proton is 1.67x10^-24g and the elementary charge is 1.602x10^-19 C, what approximately is the charge of 1 g of protons?
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10^5 C
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There are four main charge conduction categories for materials
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d) insulator, conductor, semiconductor, and superconductor
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These materials allow current to flow through them easily
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b) conductors
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The electricity and magnetism are now understood to be a united set of phenomena which we call
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electromagnetism
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What are contact forces?
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Forces so short range that macroscopically they require bodies to physically TOUCH in order to act. All everyday contact forces are ELECTROMAGNETIC force manifested by macroscopic matter.
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The formula F=kq1q2/r^2 x rhat where k=8.987 x 10^9 is _______ law.
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Coulomb's Law
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For two point charges to exert a coulomb force on eachother
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b) both must be charged
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The electrostatics force and gravity are both ________ laws
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inverse square laws
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If the distance between charges is changed by a MULTIPLICATIVE factor of 1/4, the magnitude of electric force between the charges changes by a MULTIPLICATIVE factor of
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16
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Coulomb's law and point-mass gravitational formula Fg/Fc
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c) 3 x 10^-43
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Charge separation in an object is called
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polarization
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The electric field is a
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vector field that emanates from charge (but not only charge) and causes the electric force.
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A curve through space that is tangent to the electric field vector at each point is a/an
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electric field line
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The force on a charge q caused by and electric field E is given by
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F=qE
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The force F is ________ on the distribution and in the absence of any other net external force dictates _______ of the distribution.
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the net electric force
center of mass acceleration |
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A self propogating electromagnetic field is
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light
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In the equation E = kq/r^2 x rhat
rhat is an |
radially outward pointing vector
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What is the discrete charge electric field formula for _________
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a huge charge distribution
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The force is now ___________.
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-qE, qE
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The electric field around a localized distribution of charge (with a nonzero net charge) in the far field limit looks like the electric field of a/an
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b) point charge
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Integral Sum
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an electric dipole moment.
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All finite charge distributions have a dipole moment , but usually only one with a nonzero dipole moment and that is overall neutral is called a
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dipole
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E = Crazy Bracket Dude
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Dipole moment electric field
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The far field electric field of an electric dipole falls off as:
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1/r^3
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The pattern of the electric field lines about a dipole viewed in a cross section through the dipole axis sort of:
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butterfly-like.
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The permanent or induced dipoles at the microscopic level are:
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common
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The torque on an electric dipole of dipole moment p in an electric field E is:
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t = p x E
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An electric dipole in an electric field E has a potential energy of alignment
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b) PE = -p x E
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Hugest Question Ever
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Theta not sin(wt)
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Gauss's law gives a way to easily obtain a formula for the electric field of a charge distribution in cases of:
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a) high symmetry: principally, planar, cylindrical and spherical symmetry
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To say that two physical laws or postulates are equivalent means
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a) that EACH implies the other. Thus EVERYTHING that can be deduced from one can also be deduced from the other. Coulomb's law Gauss's law in electrostatics ARE and example of equivalent laws.
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(integral) surface E dA
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electric flux through a surface
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(integral) surface E dA = qenclosed/sigmanot
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b) the integral equation form of Gauss's law.
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Spherically symmetric
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E = qencl/4piEnotr^2
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Cylindrically symmetric
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E = (lambda)encl/2piEnotr
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outside of an electrostatic conductor
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E = sigmaencl/Enot, where sig enclosed is area charge density
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Where is all the net charge on a conductor in an electrostatic situation?
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Spread (in a general non-uniformly) over the surface
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Shielding container
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Faraday Cage
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Ben franklin ideal ben
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the electric FORCE on the bits in the tankard was apparently zero and thus the electrostatic force obeyed an INVERSE-SQUARE law
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The electric potential per unit charge is the electric
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potential
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units of electric potential
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Volts
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it is the energy an elementary charge aquires if accelerated through a 1 V potential
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electronvolt or eV
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electron accelerated through a potential difference of 100v, kinectic energy in eV
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100 eV
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Say and electron is accelerated from rest through a 1 V potential. What is it's final speed?
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6 x 10^5 m/s
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If you go around any closed path in an electric field your change in electric potential is
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0 V
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The potential of a point charge (relative to infinity) is:
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V = kq/r
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a conductor in an electrostatic case is a _________ object.
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equipotential
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The difference dV in electric potential along a differential bit of path ds in the electtric field E of a positive point charge is given by
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dV = -E x ds = -E x dr
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A magnetic field is a:
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vector field that emanates from charge
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They have no ends and at every point along them the magnetic field vector is tangent to them and points in their direction
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magnetic field lines
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Magnetic field lines tend to be
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loopy
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The main reason for regarding electric and magnetic fields as actual things and not just descriptive devices for calculating electric and magnetic forces is that
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they are so useful as descriptive devices
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a region from which field lines emerge is a ; to which they go in is a .
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north pole; south pole
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The magnetic pole mnemonic is:
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likes repel; unlikes attract
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On the earths surface, a fairly large magnetic field would be
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1 T
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Magnetism has been known of probably since prehistory, with natural magnets like
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magnetite or lodestone (Fe3O4)
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The first useful device to use magnets was
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the compass
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the north magnetic pole is at
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a magnetic south pole
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The first person to suggest the earth was a magnet as
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William Gilbert
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Magnetic force law for a point charge is =
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F=qvxB
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Charged particles in magnets move in
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circles or helixes
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Discovery of the electron
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J.J. Thomson
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The hall effect showed that
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the charge carriers in metals had a negative charge
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Parallel current carrying wires will attract if the currents are parallel, which you can remember using which rule?
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a right hand rule
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A long coil of wire with a current running through it and a nearly constant magnetic field
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Solenoid
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A material in which the atomic scale magnetic dipoles can create a magnetic field
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e) magnetic material
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Magnetic materials that DONT remain magnetized are
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SOFT
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in the abscence of time varying electric fields, magnetic fields are caused by
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currents and elementary particle magnetic dipoles
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The Biot-Savart Law is
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dB= longest equation
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Amperes law is
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differential with B in it
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Magnetic field lines about an infinite wire are determined by
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a right hand rule where the thumb aligns with current
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A railgun is a
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magnetic launching device
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Faradays law of induction implies that time varying induce .
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magnetic fields; electric fields
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Faradays law of induction is
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double integral
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Magnetic flux is defined by the formula
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d(crazy symbol) = bxda
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The units of magnetic flux are
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webers
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The magnetic flux through a planar area segment
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dot product A and B
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The law talking bout induced magnetic fields
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Lenz's Law
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sense of polarity of induced around closed path in the y-z plane
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counterclockwise looking the positive x direction
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an inductor is a device designed to
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have a large SELF INDUCED EMF when a time varying current PASSES through it
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in an RC circuit the potential across the capacitor is proportional to the integral of current in an RL it is
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proportional to the derivative of current
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An inductor resists rapid changes in:
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the current through it
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An important use of an LC oscillator is
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radio emission
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The 4 Fundamental laws of electrodynamics
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e) maxwells laws
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the displacement current is
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(e) when you add a term to Amperes law to account for magnetic fields
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From his equations Maxwell found that
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light was electromagnetic waves with phase velocity c=1/ not root LC
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Electromagnetic waves are
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TRANSVERSE waves with the electric and magnetic field vectors PERPENDICULAR to each other
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