Alternating Current (Part 1)
1) What is an alternating current?
ANSWER) The current whose magnitude undergoes a definite cycle of change during a definite interval of time is known as alternating current.
2) What is a cycle?
ANSWER) A cycle is the complete change in the value and direction of an alternating quantity.
3) What is a waveform?
ANSWER) A waveform is the plot of instantaneous values of the varying quantity with time.
4) How many electrical degrees are there in a cycle?
ANSWER) 360
5) What are electrical degrees?
ANSWER) If a conductor moves in a two pole machine through 360 mechanical degrees, it is supposed to generate 360 electrical degrees.
6) What is the relation between electrical degrees and mechanical degrees?
ANSWER) θe = (P/2) θm
where θe is electrical angle, θm is mechanical angle and P is the number of poles.
7) Define frequency
ANSWER) The number of cycles per second is called frequency.
8) What is the unit of frequency?
ANSWER) The unit of frequency is Hertz (cycles/second).
9) What is time period?
ANSWER) It is the time taken to complete one cycle.
10) How frequency and time period are related?
ANSWER) T=1/f
where T is time period and f is frequency.
11) What is wavelength?
ANSWER) It is the linear distance travelled by a wave during one cycle.
12) What is velocity of propagation?
ANSWER) It is the velocity with which a wave travels. In an electric circuit it is given by:
V=1/ √ LC
where V is velocity of propagation, L is the inductance of the path through which wave is travelling and C is the capacitance of the path.
13) Describe the relation between wavelength, frequency and velocity of propagation.
ANSWER) f = v. λ
where f is frequency, v is the velocity of propagation and λ is the wavelength.
14) What is the supply of frequency in Asian countries?
ANSWER) It is 50 Hz
15) What is the supply of frequency in North America?
ANSWER) It is 60 Hz
16) Why is frequency limited to 50/60 Hz?
ANSWER) If frequency is too low then the problem of flickering will occur and if frequency is too high then the problem of iron losses will occur.
17) What is peak value?
ANSWER) It is the maximum value which an alternating quantity attains. It is also called the amplitude of the quantity.
18) What is average value?
ANSWER) It is the average of all instantaneous values during a positive or negative half cycle.
19) What is RMS value?
ANSWER) It is the effective value of an alternating quantity which if applied to a given circuit for a given time will expend same energy as when DC supplied to the same circuit will expend.
20) How is RMS value related with peak value?
ANSWER) Irms = 0.707 Imax
ANSWER) The current whose magnitude undergoes a definite cycle of change during a definite interval of time is known as alternating current.
2) What is a cycle?
ANSWER) A cycle is the complete change in the value and direction of an alternating quantity.
3) What is a waveform?
ANSWER) A waveform is the plot of instantaneous values of the varying quantity with time.
4) How many electrical degrees are there in a cycle?
ANSWER) 360
5) What are electrical degrees?
ANSWER) If a conductor moves in a two pole machine through 360 mechanical degrees, it is supposed to generate 360 electrical degrees.
6) What is the relation between electrical degrees and mechanical degrees?
ANSWER) θe = (P/2) θm
where θe is electrical angle, θm is mechanical angle and P is the number of poles.
7) Define frequency
ANSWER) The number of cycles per second is called frequency.
8) What is the unit of frequency?
ANSWER) The unit of frequency is Hertz (cycles/second).
9) What is time period?
ANSWER) It is the time taken to complete one cycle.
10) How frequency and time period are related?
ANSWER) T=1/f
where T is time period and f is frequency.
11) What is wavelength?
ANSWER) It is the linear distance travelled by a wave during one cycle.
12) What is velocity of propagation?
ANSWER) It is the velocity with which a wave travels. In an electric circuit it is given by:
V=1/ √ LC
where V is velocity of propagation, L is the inductance of the path through which wave is travelling and C is the capacitance of the path.
13) Describe the relation between wavelength, frequency and velocity of propagation.
ANSWER) f = v. λ
where f is frequency, v is the velocity of propagation and λ is the wavelength.
14) What is the supply of frequency in Asian countries?
ANSWER) It is 50 Hz
15) What is the supply of frequency in North America?
ANSWER) It is 60 Hz
16) Why is frequency limited to 50/60 Hz?
ANSWER) If frequency is too low then the problem of flickering will occur and if frequency is too high then the problem of iron losses will occur.
17) What is peak value?
ANSWER) It is the maximum value which an alternating quantity attains. It is also called the amplitude of the quantity.
18) What is average value?
ANSWER) It is the average of all instantaneous values during a positive or negative half cycle.
19) What is RMS value?
ANSWER) It is the effective value of an alternating quantity which if applied to a given circuit for a given time will expend same energy as when DC supplied to the same circuit will expend.
20) How is RMS value related with peak value?
ANSWER) Irms = 0.707 Imax
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