The process of inducing a voltage in a conductor by passing it through a magnetic field.
One revolution of an AC generator.
(Also, two complete alternations of voltage with NO reference to time.)
Sine wave values (pair of numbers)
Degree of rotation- armature's position in the field.
Amplitude-value in relation to maximum or minimum.
Absolute value (no negative numbers) of the point of greatest magnitude. (The peak of the curve-positive or negative)
The amount that produces the same degree of heat in a given resistance as an equal amount of DC.
The number of cycles that occurs in a specific period of time.
(Usually cycles per second)
(Square wave) The duration that the voltage is at the max or min amplitude. Pulse width is one half of the period-hence square.
Triangular wave harmonics
Fundamental frequency and all ODD harmonics AND all are 180 degrees out of phase.
How is AC current measured with a moving coil meter?
The AC current must first be converted to DC.
Clamp on ammeter
A split core transformer. It is clamped around the conductor and uses the voltage induced by the conductors magnetic field
Oscilloscope provides the following data:
Phase relationship (of 2 or more waveforms)
Shape of a waveform
Parts of an oscilloscope:
Cathode Ray Tube
Horizontal deflection amp
Vertical deflection amp
Phase relationship such that current and voltage pass through peaks and zeros at the same time.
Purely resistive circuits are
IN PHASE. Voltage and current pass through max and zero at the same point.
Does current flow across a capacitor?
NO! The capacitor charging and discharging results in movement of electrons from one plate to the other. This resembles current flow.
Capacitive Circuit Operation
Voltage starts from zero. Capacitor is empty. Current becomes max. Capacitor charges. Current drops as voltage becomes max and capacitor nears full charge. At max voltage capacitor is fully charged & current drops to zero. Voltage drops towards negative. Capacitor opposes and negative current flows as capacitor discharges.
RC Low Pass Operation
Allows low frequencies to pass while attenuating high frequency. At low frequency, capacitive reactance is HIGH so voltage drop is across capacitor.
RC High Pass Operation
Allows high frequency to pass while attenuating low.
At high frequency, capacitive reactance is LOW so voltage drop is across the resistor.
Counter Electromotive Force (CEMF)
Voltage induced in an inductor coil which opposes the applied voltage. It is out of phase by 180 degrees.
Factors effecting CEMF
The greater the rate of change of the magnetic field (faster the magnetic field expands or collapses) the greater the CEMF.
RC Low pass filter - Memory Trick
Capacitor low = frequency low
(Capacitor low in schematic. Low frequency passes)
RC High pass filter - Memory Trick
Capacitor high=frequency high
(Capacitor high in schematic. High frequency passes)
Leading Output Phase-Shift Network
Look for C. (C slows voltage) C in back - input slow-output leads. Output voltage leads input voltage.
Lagging Output Phase-Shift Network
Look for C. (C slows voltage) C in front-output slow-input leads. Output voltage lags input voltage.
Why is the capacitive voltage vector (Ec) drawn downward?
It lags current by 90 degrees. This is why it points down (-90 degrees).
Why are current vectors used to analyze a PARALLEL circuit?
Because the VOLTAGE is the SAME across all components.
All are EQUAL and IN PHASE with current, so that vector is the horizontal (X) axis.
Why are voltage vectors used to analyze a SERIES circuit?
Because the CURRENT is the SAME across all components.
All are EQUAL and IN PHASE with voltage, so that vector is the horizontal (X) axis.
The ratio of true power (in watts) to apparent power (in volt-amperes) in a REACTIVE circuit.
The value of capacitive reactance _______ as frequency increases
decreases (inversely proportional)
High freq=low Xc
Counter electromotive force (cemf)
Voltage induced in an inductor coil by the expansion and collapse of the magnetic field resulting from an applied voltage.
Always opposes applied voltage.
Greater inductance=greater cemf
Always 180 degrees out of phase with applied voltage.
In a purely inductive circuit current ___ voltage.
LAGS - remember ELI the ICE man.
E(voltage) L(inductive circuit) I(current)
Current lags by 90 degrees.
The opposition to current flow by an inductor in an AC circuit is
inductive reactance (Xl) measured in ohms
Inductive reactances in series
When inductors are connected in series, the total inductive reactance is equal to the sum of the individual inductive reactance values