Alternating Currents Flashcards
What is the period (T) of an alternating current?
The time taken for one complete cycle of the alternating current.
What is the frequency (f) of an alternating current?
The number of oscillations per unit time.
What is the relation between frequency and period?
f= 1/T
What is the peak value of an alternating current or voltage?
The highest point on the graph of the current or voltage.
What is instantaneous current (πΌ) or voltage (π)?
The value of current or voltage at a particular instant in time (π‘).
What are the equations for instantaneous current and voltage?
I=I 0 sin(Οt), π = π 0 sin(ππ‘)
What is the angular frequency (π) of an alternating current?
Ο = 2Οf = 2Ο/T
β
What is the r.m.s value of current or voltage?
The steady current or voltage that produces the same power in a resistor as the alternating current or voltage.
How is r.m.s. current (πΌ rms) related to peak current (πΌ 0)?
I rms = I 0/ β2
How is r.m.s. voltage ( π rms ) related to peak voltage (π 0)?
V rms = V o / β2
What is the equation for power in an a.c. circuit?
P = IV
How is power related to r.m.s. values of current and voltage?
P = (I rms) (Vrms)
What is the relation between peak power and average power in a sinusoidal a.c. circuit?
Peak power is twice the average power: P = 1/2 (I o * Vo)
What are eddy currents?
Circular electric currents induced in a metallic conductor moving in a magnetic field.
What is the effect of eddy currents?
They oppose the change in flux (Lenzβs Law) and cause energy loss as heat.
Why is electricity transmitted at high voltage?
To reduce current, minimizing heating and voltage loss in wires.
Why is a.c. used for transmission?
Because a.c. voltage can be changed efficiently using transformers.
What is half-wave rectification?
Only one half of the a.c. cycle is used, reducing the power output.
What is full-wave rectification?
Uses a bridge diode to rectify both halves of the a.c. wave.
What is the function of a smoothing capacitor?
It charges during the rising wave and discharges during the falling wave to smooth the rectified voltage.
What happens if a small capacitor is used in smoothing?
It discharges rapidly, leading to more ripples in the output voltage.
What is the time constant (πΆπ ) of a capacitor-resistor circuit?
The time taken for charge to fall to 1/e (about 37%) of its original value.
How should the time constant be compared to the a.c. period for effective smoothing?
It should be much greater than the a.c. time period to prevent significant discharge.
