FW Quiz 2
Gauss's Law Problem
Do Integral D * ds = Qencl (flux density multiplied by surface area = Qencl) Qencl = charge density * length, surface area, or volume D = εE for perfect conductor: D = 0 and E = 0
Image Method Problem
Draw charges that are equal and opposite on the opposite side of the conducting plane. electric field lines: positive to negative equipotential lines: oblong shape, close to the charge on the closest to the conducting plane and far away from charge on side away from conducting sphere highest charge density where charge sphere and conducting plane face each other
Either electric field or magnetic field exerts force on a moving charge and changes the charge's energy.
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T/F All capacitors leak and cannot be used to store electromagnetic energy for any application; inductors are used instead.
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T/F An electric field drives charges moving in a conductor to produce a current, which can always produce a magnetic field, which can then always produce an electric field opposite to the original electric field.
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T/F Any given charge configuration above an infinite perfectly conducting ground plane is electrically equivalent to the combo of the given charge config and its image config plus the charges induced on the ground plate.
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T/F Electrical energy stored in a capacitance depends on the material properties and geometries, but not on the electric field.
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T/F Faraday's Law is the electric Kirchhoff's voltage law for a circuit with a voltage source while Ampere's Law is equivalent to electric Kirchhoff's voltage law and can be used to solve the magnetic circuit problems.
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T/F Gaussian surface is constructed based on the charge distribution, so that the electric field flux density is always perpendicular to the Gaussian surface.
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T/F Magnetic circuit, analogous to electric circuit, can be used to accurately solve magnetic field problems involving current coils, ferromagnetic cores and air gaps
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T/F The eddy current induced by a time varying magnetic field produces a magnetic field, which is always opposite to the magnetic field that induces the eddy current
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T/F The magnetic field lines always start from the north pole and end at the south pole.
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T/F The vector potential can be measured with an inexpensive meter, just like the electric scalar potential.
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T/F Laplace's Equation becomes Poisson's Equation in any region with no volume charge.
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T/F E-field lines and equipotential surfaces are never perpendicular to each other
F (they are always perpendicular)
Magnetostatics Problem (solenoid)
H = znI B = μH Φ = B *S L = Λ/I = NΦ/I Wm = 0.5LI^2
Ampere's Law Problem
Integral H *dl = Inet H * 2*pi*r = = Inet if there is a conducting cylinder H is not the same everywhere ex: for cylinder with radius a Inet = (pi*r^2/pi*a^2 )* I for r<a Inet = I for r>a B = μH ∇ x A = B dAz/dr = B guess something for A so that when you take the derivative it is equal to the B field you found earlier L12 = Λ12/I1 = NΦ/Inet Φ = integral B*ds for an iron ring around a cylinder ds = wdr where w is the width of the iron ring
T/F Amperian contour is analogous to the Gaussian surfaces and defines an open surfaces
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T/F Biot-Savart's law is used in magnetostatics, analogous to Coulomb's law in electrostatics: they can be used to determine the field intensity.
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T/F Electric field lines always begin from positive charges and end on negative charges
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T/F For a system consisting of conductors and dielectrics, its resistance and capacitance do not depend on electric field; they depend on the material properties and geometries.
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T/F For typical simple geometry of a magnetic system, the magnetic system, the magnetic vector potential direction is parallel to the current direction
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T/F Gauss's Law in electrostatic does not involve electrical properties of the material while Ampere's law does not involve magnetic properties of the materials
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T/F Gauss's law describes the divergence of the electric field, while Ampere's Law describes the rotational property of the magnetic field.
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T/F Gaussian surface must be a closed surface and encloses a volume
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T/F If the right hand thumb points along the current the directions the curved four fingers indicate the field direction
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T/F Magnetic properties of materials tend to be either very strong or very weak.
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T/F The free net charges of a perfect conductor can appear only on the surface
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T/F The magnetic field lines are always closed loops without a start or end
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T/F The magnetic susceptibility of a diamagnetic material is a negative constant
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T/F The magnetic vector potential can be used to determine the magnetic flux.
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T/F When using finite difference method to solve Laplace's equation in a uniform medium, the potential of a given point equals the average of the values at its nearest neighboring points.
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T/F With finite difference method, a Dirichlet boundary means that a fixed voltage is given at the boundary, while Uniform Neumann boundary means that the boundary voltage equals the value of its immediate inside neighbor.
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T/F the solutions to Laplace's equation in some region in space is not unique unless a voltage is specified at some location.
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Faraday's Law
Vemf = (-d/dt integral B*s) Vemf = -N dΦ/dt
Magnetic Circuits Problem
the "voltage" is NI the "current" is Φ Place a reluctance for every gap and the material R = l/μS S is kinda like area, l is mean length B = Φ / S L = Λ/I = NΦ/I = NBS/I Wm = 0.5LI^2
Poisson/Laplace and Capacitance Problem
∇^2V = -ρ/ε ∇^2V = 0 if no charge in cylindrical: ∇^2V = 1/r* d/dr(r*dV/dr) = 0 rdV/dr C1 V(r) = integral C1/r dr = C1*ln(r) + C2 @ r=a, V = Vo @ r=b, V = 0 E = -∇V D = εE ρs = D1n Q = surface area *ρ C=Q/Vo We = 0.5CV^2