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29 Cards in this Set
- Front
- Back
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What is symbol and units for Magnetic Flux?
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Φ , Webers (Wb)
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What is the Symbol and unit for flux density?
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B , Teslas (T)
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A magnetic field is a _____ field.
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force
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With Faraday's flux concept, the density of lines represents the _____ of the field and their direction represents the _____ of the field.
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strength, direction
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Three ferromagnetic materials are what?
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Iron, nickel, and cobalt
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The direction of a magnetic field is from ____ to ____ outside a magnet.
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North, South
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True or False. Plastic has a an effect on a magnetic field, but much smaller than iron.
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False. Plastic has no effect.
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Flux density B is defined as the ratio Φ/A, where A is the area _______ to Φ.
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Perpendicular
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To figure out the direction of the magnetic field about a current-carrying conductor, use the ____ hand rule, where your _____ points in the direction of the current.
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Right, Thumb
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Define fringing
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A decrease in flux density in an air gap between two ferromagnetic materials.
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What is the "stacking factor"?
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The ratio of ACTUAL area of ferrous material to the PHYSICAL area of the core.
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What does the symbol "H" stand for and what are it's units with respect to magnetism?
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Magnetic Field Intensity, Ampere-turns/length (At/m)
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What symbol represents Magnetomotive Force or MMF?
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£ <- supposed to be cursive F
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How are H and £ related?
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H=£/l (magnetomotive force / length)
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What happens to H (Magnetic Field Intensity) when the core's length increases?
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It decreases
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Permeability is a measure of how ____ it is to establish flux in a material.
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easy
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Define Reluctance.
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The opposition to flux in a magnetic circuit.
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How do £ (magnetomotive force), Number of turns in a coil, and I (current) relate?
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£=NI
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How do B (flux density) and H (magnetic field intensity) relate?
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B=μH where μ is permeability
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How is RMS voltage calculated for any waveform?
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squareroot of area under v squared curve divided by the base
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Why are most cheaper multimeters not accurate when calculating non-sinusoidal RMS waveforms?
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(average responding meters) They rectify AC to DC. Then take the average value and use a multiplier to calculate RMS- only works for sine waves.
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How is the effective value calculated given an AC signal added to a DC signal?
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Square root of AC squared plus DC squared. (Distance formula)
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What does j*j= ?
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-1
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What are the units for reactive power?
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VAR (volt-amps reactive)
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How do you total the power in a parallel circuit?
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By summing- same for series
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What is the symbol for Apparent Power and units?
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a. S
b. VA (volt-amps) |
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How is the Power Factor calculated?
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Fp = P / S
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Define Eddy Currents.
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Unwanted current that is induced in the core of an inductor or transformer by changing core flux.
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Define Hysteresis.
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Power loss in a ferromagnetic material caused by the reversal of magnetic domains in a time varying magnetic field.
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