Alternating Voltages And Current Flashcards
What are reasons for the choosing DC over AC in electric power generation and distribution
It is more cheaper to generate, It can easily be converted from one voltage level to another with transformers
What device converts AC to DC
Rectifier
What are the two Faraday’s laws of electromagnetic induction
When there is a change in flux, EMF will be induced in a coil. The rate of change of flux is directly proportional to the induced EMF
What is a waveform
It is a graphical representation of the variation of a physical quantity with time
When is a waveform referred to as alternating
When their quantities are constantly changing in direction
What is a period
The total time taken for a quantity to complete one cycle
What is a cycle
One complete series of values
What is frequency
The number of cycles completed in one second
What are Instantaneous values
These are values of alternating quantities at any instant of time (v, i)
What is the peak value
This is the largest value in half a cycle (Vm, Im)
What is the average or mean value
The average value measured over half a cycle
What is the formula for calculating average value for a sine wave
0.637(2/pi) * maximum value
What is the effective/Root Mean Square value of an alternating current
It’s the current that will produce the same heating effect as an equivalent direct current (I, V)
What is the formula for calculating rms value for a sine wave
sqrt(2) * maximum value
What does form factor and peak factor do
They give an indication of the shape of a waveform. Form Factor = ms/average value, Peak factor = max/rms
What is phi in sine waves
This stands for phase difference. +Phi leading, -Phi lagging
What is the equation of sinusoidal voltage
v = Vmsin(wt + or - phi)
What is the value of phi in v = Vmsin(wt + or - phi)
The angle of lead or lag compared to Vmsin(wt)
What is the process of rectification
This is a process of obtaining unidirectional currents and voltages from alternating currents and voltages
What are the different types of rectification
Half wave, Full wave with center-tapped transformer, Full wave with bridge
How is smoothing of rectifier output usually done
Capacitor is connected across the output. It stores and releases charges between the peaks of rectified waveform
What’s the relationship between voltage and current in a purely inductive circuit
I lags V by 90 degrees
What’s the opposition to the flow of current in a purely inductive circuit usually called
Inductive reactance
What’s the relationship between voltage and current in a purely capacitive circuit
I leads V by 90 degrees
