A1 LT19 + 20 Flashcards
What is faradays law
when conductor is moved relative to a magnetic field, a voltage is induced in the conductor.
Formula for magnetism
e=Blv
e = voltage generated
B = flux density
l = length of conductor in the field
v = relative velocity if the conductor at right angle to the field
What is a prime mover
the device supplying the energy to the generator
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.
or
For every action there must be an equal and opposite reaction
What does each finger point to in flemings left hand generator rule
thumb = motion of conductor
pointer finger = direction of field
middle finger = direction of electron current
The magnitude of induced voltage is dependent on
the rate at which the conductor cuts the flux lines
Slip rings are for AC or DC generators?
dc
Split rings are for AC or DC generators
AC
at what two degrees does a generator not induce any voltage
0 and 180
How many degrees of an electrical waveform make up one cycle
360
what is the formula for frequency
f=PxN/120
f= frequency
P= number of poles
N=speed of alternator in rpm
biggest benefit of AC generators of dc
can produce a much high voltage
WHy would you use AC over DC (3)
AC can be stepped up and down easily and effectively
Motors and controls are usually simpler, smaller, cheaper and more reliable.
AC motors dont need brushes like DC motors
What Periodically changes in both magnitude and direction
AC current
What is a cycle
The distance from one point on a waveform to where it starts to repeat itself is a cycle
Each cycle consists of 360 electrical degrees
One cycle corresponds to one complete rotation of the conductor in the magnetic field
What is the average value of a sine wave
Zero
What is a alternation
One alternation on an AC waveform is that part of the wave from where it crosses the x-axis to where it crosses the axis again
What is a period
The period (p) of a waveform is the time it takes to complete one cycle
The period of a waveform is equal to the number of seconds per cycle
What is frequency
The frequency (f) of a waveform is the number of complete cycles that occur in one second, measured in cycles per second or hertz
What is amplitude
The maximum height of the waveform above or below the axis
At what two degrees does peak value occur
90 and 270
What is peak to peak value
The difference between the positive peak value and the negative peak value
Formula for instantaneous value
e=(peak value)x(sine of angle)
What is effective value
The effective value of an AC waveform is equal to the value of DC source that would give the same heating effect in a resistive load
How do you find effective value
rms = 0.707 X peak value
What is the peak value that comes from a 120v wall receptical
170v
