Test Review Flashcards
Inductors always _______ a change in current.
Oppose
When current flows through a conductor, what is created?
Magnetic field
What are the important factors concerning electromagnetic induction?
- a conductor
- relative motion
- magnetic field
An induced voltage or current _______ the motion that causes it.
Opposes
Lenz’s Law
What is the greatest advantage of AC?
It can be transformed
The _______ must be found when a sine wave AC voltage is changed into DC with a rectifier?
Average
What is the formula to find RMS value?
RMS = peak * .707
Resistive loads are characterized by the fact that they…
- produce heat
- voltage and current are in phase
A sine wave contains _______ degrees.
360
What is a line that indicates both magnitude and direction?
Vector
What is the formula for instantaneous voltage?
E (isnt) = E(max) * sin(theta)
What three factors determine the amount of voltage induced?
- number of turns of a wire
- strength of magnetic flux (flux density)
- speed of cutting action
Each complete waveform of 360 degrees is called a _______.
Cycle
What is the sum of all angles of a triangle?
180 degrees
What is the unit of measurement for inductance?
Henrys (H)
The amount of inductance on a coil is determined by what two things?
- space between the windings
- physical properties and construction
What is the most common of all AC waveforms?
Sine wave
The _______ of the induced voltage can also be changed by reversing the _______ of the magnetic field.
Polarity; polarity
What does RMS stand for?
Root mean square
What is the formula to solve for RMS value?
RMS = peak * .707
What is a cycle?
A complete waveform
What can AC do that DC cannot?
Transform
Vector is a line that determines _______ and _______.
Magnitude; direction
What is the Pythagorean theorem?
c^2 = a^2 + b^2
What is a Henry?
Unit of measurement for inductance
_______ always oppose a change of _______.
Inductors; current
_______ opposes the motion that causes it.
Induced voltage
What is a voltage spike?
When current flow through an inductor stops, and the current also decreases at an exponential rate
1 Weber = _______ lines of flux
100,000,000
The _______ describes the rate of certain occurrences and is divided into _______ time constants
Exponential curve; 5
During each time constant, how much does the current rise?
63.2%
What is electromagnetic induction?
When a conductor cuts through magnetic lines of flux, a voltage is induced into the conductor.
The number of cycles completed in one second is called?
Frequency
What type of wave is the triangle wave?
Linear wave
What electronic component is often used to prevent large voltage spikes from being produced when the current flow is terminated?
Diode
Induced voltage is always _______ in polarity to the _______ voltage.
Opposite; applied
What opposes a change of current?
Inductors
Inductors can produce _______ when the current stops flowing through them.
Voltage spikes or extremely high voltages
What are two devices to help prevent large spike voltages?
Resistors and diodes
In an R-C circuit, the current flow through the capacitor will be _______ out of phase with the current flow through the resistor.
90 degrees
In a parallel connected R-C circuit, the voltage will be _______ through all devices.
The same
In an AC R-L circuit, the total current I is equal to the applied voltage divided by _______.
Impedance (Z)
When AC voltage is being measured with a voltmeter, which value of AC voltage will be indicated?
RMS
How many degrees are there in one complete cycle of alternating voltage?
360
A sine wave has a peak or max value of _______ voltage. (What is the formula)
E (inst) = E(max) x sin(theta)
What best describes average voltage?
The amount of voltage that would be measured by a DC voltmeter after a sine wave AC voltage has been rectified with a full wave rectifier.
What best describes RMS voltage?
The amount of AC voltage that will produce as much power as a like amount of pure DC voltage.
What is the relationship of current and voltage in a pure resistive circuit?
In phase
Vectors are lines that indicate…
Magnitude and direction
What is the relationship of current and voltage in a pure conductive circuit?
Current leads voltage by 90 degrees
What would limit the amount of current flow in a pure inductive circuit?
Inductive reactance
What three factors determine the amount of capacitance a capacitor will have?
- surface area of plates
- distance between the plates
- type of dielectric used
What is the unit of capacitance?
Farads
What is the total resistance in a purely inductive circuit called?
Inductive reactance
