Page 28 - 12-phy-16 ALTERNATING CURRENT

16. Alternating Current eLearn.Punjab

SUMMARY

• Alternating current is that which is produced by a voltage source whose polarity keeps on

reversing with time.
• The time interval during which the voltage source changes its polarity once is known as period T

of the alternating current or voltage.
• The value of voltage or current that exists in a circuit at any instant of time is known as its

instantaneous value.
• The highest value reached by the voltage or current in one cycle is called the peak value of the

voltage or current.
• The sum of positive and negative peak values is called peak to peak value and is written as p-p

value.
• The root mean square value (rms) is the square root of the average value of V or / .
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• The angle q which specifies the instantaneous value of the alternating voltage or current, gives
the phase lag or phase lead of one quantity over the other.

• An inductor is usually in the form of a coil or a solenoid wound from a thick wire so that it has a
large value of self inductance and has negligible resistance.

• The combined effect of resistance and reactance in a circuit is known as impedance and is
denoted by Z.

• Choke is a coil which consists of thick copper wire wound closely in a large number of turns over
a soft iron laminated core.

• Electromagnetic waves are those which require no medium for transmission and can propagate
through vacuum.

• Modulation is the process of combining the low frequency information signal with a high
frequency radio wave, called carrier waves. The resultant wave is called modulated carrier wave.

QUESTIONS

16.1 A sinusoidal current has rms value of 10 A. What is the maximum or peak value?
16.2 Name the device that will (a) permit flow of direct current but oppose the flow of

alternating current (b) permit flow of alternating current but not the direct current.
16.3 How many times per second will an incandescent lamp reach maximum brilliance when

connected to a 50 Hz source?

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