In this section, you will find objective questions related to AC Fundamentals which helps to analyze the networks consisting of various alternating current and voltage sources, resistances and inductive, capacitive reactances.
- The form factor in reference to alternating current wave form represents the ratio of the R.M.S. value to the average value.
- If the current and voltage are out of phase by 90°, thee power is Zero.
- The form factor of a 220 V, 50 Hz A.C. waveform is 1.11.
- If E1 = A sin 𝜔𝑡 and E2= A sin (𝜔𝑡−𝜃) then E1 leads E2 by𝜽.
- For the waveform shown in figure, average value is 1.5 A.
- For the above wave the rms value will be 1.528 A.
- Two sinusoidal quantities are said to be phase quadrature, when their phase difference is 𝟗𝟎°.
- The equation for 25 cycles current sine wave having rms value of 30 amperes, will be 42.4 sin50πt.
- R.M.S value of a current given by 𝑖=10+5 cos (628𝑡+90°) is 10.6A
- What is the rms value of rectangular voltage wave with an amplitude of 10 V? 10V.
- The mean value of a.c related to peak value of a.c by the equation is 𝑰𝒎= 𝟐𝑰𝒐𝝅.
- In above case , the value of direct current which produces in the same conductor the same amount of heat in the same time will be 141 V.
- The current in a circuit follows the law 𝑖=100sin𝜔𝑡, If the frequency is 25 Hz how long will it take for the current to rise to 50 amperes? 𝟏𝟏𝟎𝟎𝟎 sec.
- The voltage 𝑣=90cos(𝜔𝑡−161.5°) may be represented as sine function by 𝟗𝟎𝐬𝐢𝐧(𝝎𝒕−𝟕𝟏.𝟓°).
- The equation of emf is given by =𝑰𝒎√(𝐑𝟐+𝟒𝛚𝟐𝐋𝟐) .
- In above problem the frequency in hertz is 𝝎𝝅.
- The negative maximum of a cosine waveform occurs at 180°.
- The RMS value of sinusoidal 200 V peak to peak wave is 𝟐𝟎𝟎√𝟐 v. ???
- The positive maximum of a sine wave occurs at 𝟗𝟎°
- In figure 4 the combined impedance of the parallel circuits equals 120 V.
- For the same peak value of voltage, which waveform will have the least rms value? Triangular wave.
- For the same peak value of voltage, which waveform will have the highest rms value? Square wave.
- Which wave has the highest value of form factor? Half wave rectified sine wave.
- Which wave has the least value of form factor? Square wave.
- Which of the following waves has form factor of 1.0? Square wave.
- If one cycle of ac waveform occurs every milli-second, the frequency will be 1000Hz.
- Which of the following frequencies has the longest period? 10kHz.
- RMS value and the mean value is the same in case of Square wave.
- If emf in a circuit is given by 𝑒=100sin628𝑡 then maximum value of voltage and frequency are 100V 100Hz.
- If a wave form more peaky than a sine wave, the form factor will be more than 1.11.
- For a triangular wave, the form factor is 1.15.
- For a square wave, the form factor is 1.0.
- The equation of alternating current is 𝑖=42.42sin628𝑡. the average value of current is 27A.
- For the voltage waveform shown in figure 5 the rms value of voltage will be √𝟓𝟑 𝒚 𝒎𝒂𝒙.
- The average value of the above voltage is 𝟐𝟑 𝒚 𝒎𝒂𝒙.
- The peak factor for the above voltage is 𝟑√𝟓 .
- The form factor for the above voltage is√𝟓𝟐.
Questions 38 to 40 refer to the following data:
A current has following steady values in amperes for equal intervals of time changing
simultaneously from one to the next 0, 10, 20, 30, 20, 10, 0, -10, -20, -30, -20, -10, -0.
- The rms value of the current will be 17.8 A.
- The form factor will be 1.187.
- The peak value of a wave isMaximum valuer.m.s value
- In the above case the value of which parameter for full sine wave will be more?
- An alternating voltage 𝑒 = 200 𝑠𝑖𝑛 314𝑡 is applied to a device which offers an ohmic
resistance of 200Ω to the flow of current in one direction while entirely preventing the
flow in the opposite direction. The value of current will be 5 A. ??
- In the above case, the average value of the current will be 3.18 A.
- When the sole purpose of the alternating current is to produce heat, the selection of
conductor is based on rms value of current.
- The r.m.s value of a.c. is related to peak value of a.c. by the equation 𝑰𝒐 = √𝟐 I r.m.s.
- The form factor of dc supply voltage is always Unity.
- What is the angle in the NE quadrant corresponding to a rms value of the quantity, 𝑦 =𝑦𝑚𝑎𝑥 𝑠𝑖𝑛𝜔𝑡? 𝝅𝟒.
- What is the angle in NE quadrant corresponding to the average value of the quantity,
𝑦 = 𝑦𝑚𝑎𝑥𝑠𝑖𝑛𝜔𝑡? 0.69 rad.
- Two currents represented by 𝑖1 = 50 sin 𝜔𝑡 , 𝑖12 = 100 sin(𝜔𝑡 + 45 °) are fed into
a common conductor. The rms value of the current will be between 50 A and 100 A.