D1 Flashcards
(37 cards)
What is Faradays law of electromagnetic induction?
The magnitude of the voltage induced in a turn of wire is proportional to the rate of change of flux passing through (or linked with) that turn.
What is Faradays law in a formula?
e=Blv
e = voltage generated in volts
B = flux density of the field in tesla
l = active length of the conductor in the field in metres
v = relative velocity of the conductor at right angles to the magnetic field in metres per second.
What is the active length of the conductor?
The portion of the conductor that actually cuts through the lines of flux.
What is flux density controlled by?
The magnitude of the current flowing through the field coils. Normally achieved with a rheostat.
Velocity
Controlled by adjusting the speed of the prime mover.
What is Lenz’s Law?
The direction of the induced EMF must be such that any current resulting from it will develop a flux that will oppose any change in the original flux.
Flemings Left hand rule
insert pic here
What is most commonly used to control generated EMF?
Flux density
In Flemings Left hand rule what does the thumb represent?
The motion of the conductor.
In Flemings Left hand rule what does the first finder represent?
The direction of the magnetic field.
What are the advantages of using AC?
- Alternators can be manufactured with much higher voltage and power ratings than DC.
- Alternating voltages can be easily stepped up and down.
- AC motors are generally smaller, simpler cheaper and more reliable than DC.
What are the advantages of using DC?
- Required to produce magnetic fields for alternators and synchronous motors.
- Electrochemical processes such as electroplating and battery charging require DC.
- High intensity light sources.
- precise speed control.
- DC traction motors.
What is a cycle?
The distance from one point on a waveform to where it starts to repeat itself. Consists of 360 degrees.
Alternation
One cycle contains two alternations.
What is the period of a waveform?
The time it takes to complete one cycle.
Define frequency
The number of complete cycles that occur in one second.
Peak Value
The maximum positive value or negative value of the waveform.
How do you find instantaneous value?
Einst=Epk x sin angle
Average value
Epk x .637
RMS Value or Effective value
Epk x .707
What is effective resistance?
The property of an electric circuit that dissipates electric energy.
What is effective resistance made up of?
- Pure ohmic resistance.
- Skin effect.
- Hysteresis losses
- eddy current losses
- dielectric losses
- radiation losses
What is the formula for frequency?
f= [PxN]/120
What is the formula for calculating the time constant of a capacitive circuit.
t=RC
