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What is an Isolation Transformer?
A transformer that has its secondary winding physically and electrically isolated from the primary winding.
What is the transformer?
A magnetic device that changes the voltage, current, and impedence without changing the frequency.
What are the common transfomer efficiencies?
90% to 99% full load.
Define power factor.
What is the calculation?
- Ratio of real power to apparent power.
In what form is energy of a capacitor stored\?
In what form is energy of a inductor stored?
What is a dielectric?
Define Inductive Reactance
The current limiting property of an inductor in an AC circuit.
Define Capactive Reactance
The current limiting property of a capacitor in an AC circuit
State Kirchhoff's Current Law
The sum of the currents entering and leaving a point must equal zero.
State Kirchhoff's Voltage Law
The sum of the voltage drops and voltage sources in a closed circuit must equal zero.
Name three factors that determine the amount of induced voltage in a coil.
- number of turns of wire
- strength of the magnetic field (flux density)
- speed of the cutting action
What is frequency?
The number of complete cycles per second.
List 3 factors that determine the capacitance of a capacitor.
- Surface area of the plates
- Distance between the plates
- Strength of the dielectric
Explain the current and voltage relationships from phase to line in a wye and delta.
- wye: Line voltage = root3 * phase voltage
- delta: Line current = root3 * phase current
What is the equation for power in a 3-phase load?
- Line: P = root3*V*I
- Phase: P= 3*V*I
What is a Coulomb?
quantity measure of electrons. 6.25*10^18
rate of electron flow. C/s
Electric Potential. The force that pushes electrons through a wire. J/C
Resistance to current flow (V/A)
Amount of power being used by a circuit. Energy change must occur to produce watts. J/s
How can the polarity of an electromagnet be determined if the direction of current flow is known?
Left hand rule. Thumb in the direction of the north pole. Fingers in the direction of current flow
Define Flux Density
magnetic flux lines per square inch. strength of the magnetic field.
when the magnet's strength is increased only slightly with an increase of current.
Define Residual Magnetism
The amount of magnetism left in a material after the current has stopped
What range of electric current generally causes death and how?
50-200mA. Fibrillation of the heart.
What is a ground fault?
An unintended current path to ground.
Define Ohm's Law
Mathematical relationship between voltage, current, and resistance V=IR
What determines the polarity of magnetism when current flows through a conductor?
Direction of current flow.
What determines the strength of the magnetic field when current flows through a conductor?
Amount of current.
What is a vector?
A line that indicates both magnitude and direction.
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