Midterm Review Flashcards
(32 cards)
Define lenz law
An induced voltage or current opposes the motion that causes it (switches polarity)
A Henry is a measure of?
Inductance
Define a Henry
A 1 Henry coil induces 1 voltage of current when 1 amp is applied
Define inductance
A measure of a circuits ability to induce voltage
What causes counter electro motive force (CEMF)
Caused when voltage swaps polarity
What affect does inductive reactance have on an AC circuit?
Limit current flow
Why doesn’t current rise to max ohms law value when DC is applied to an inductor?
Current gets limited by the electro magnetic field of induced voltage
What are the four ac losses
Hysteresis, eddy currents, skin affect, dielectric
Is there anytime when electrical degrees match mechanical degrees
Yes, a 2 pole generator
What happens when a coil meant to run AC gets connected to DC
Draws more current
What devices can be used to prevent voltage spikes in DC
Mov, diodes, resistor
What devices can be used to prevent voltage spikes in AC
Resistor, mov
What’s the formula to calculate RPM (NS)
Rpm (Ns) = frequency x120/number of poles
When a dc source is applied to an inductor a _____ can be inserted in _____ with the inductive load to eliminate voltage spikes
A diode in parallel
When an ac source is connected to an inductor an _____ can be inserted in _____ to eliminate voltage spikes
An MOV in parallel
What’s the formula for inductive reactance (XL)
XL=2pi x frequency x HENRY’S (Henry’s are measured in L)
Formula for EMF
EMF= L x (I/T)
Formula for RMS
Rms= epeak x 0.707
Formula for E_inst
E_inst= e_max x sin<. (< is angle)
Formula for peak 2 peak
Peak x 2
Formula for peak
Rms/0.707
Average voltage for an AC sine wave
0
Formula for time constant
L/R
I max formula
Et/r
