EMI & AC - Alternating Current

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Q. If the frequency of an AC source is 50 Hz, what is the time period of the AC signal? (2019)
  • A. 0.02 s
  • B. 0.01 s
  • C. 0.5 s
  • D. 1 s
Q. If the frequency of an AC source is increased, what happens to the inductive reactance? (2019)
  • A. Increases
  • B. Decreases
  • C. Remains constant
  • D. Becomes zero
Q. If the inductance of a coil is doubled, what happens to its inductive reactance at a constant frequency? (2022)
  • A. It doubles
  • B. It halves
  • C. It remains the same
  • D. It quadruples
Q. If the voltage across a capacitor in an AC circuit is 100 V RMS, what is the peak voltage? (2022)
  • A. 100 V
  • B. 141.42 V
  • C. 200 V
  • D. 70.71 V
Q. If the voltage across an inductor is 100 V and the current through it is 2 A, what is the inductive reactance? (2023)
  • A. 50 Ω
  • B. 200 Ω
  • C. 100 Ω
  • D. 25 Ω
Q. In a series RLC circuit, at resonance, the impedance is equal to which of the following? (2020)
  • A. Zero
  • B. R
  • C. XL
  • D. XC
Q. In a series RLC circuit, what happens at resonance? (2020)
  • A. Impedance is minimum
  • B. Current is minimum
  • C. Voltage is maximum
  • D. Power factor is zero
Q. In a series RLC circuit, what happens to the current when the circuit is at resonance? (2021)
  • A. It is maximum
  • B. It is minimum
  • C. It is zero
  • D. It is constant
Q. In a series RLC circuit, what happens to the total impedance when the circuit is at resonance? (2022)
  • A. It is minimum
  • B. It is maximum
  • C. It is equal to R
  • D. It is equal to L
Q. In an AC circuit, if the current lags the voltage by 30 degrees, what is the power factor? (2023)
  • A. 0.866
  • B. 0.5
  • C. 1
  • D. 0.707
Q. In an AC circuit, if the power factor is 0.5, what is the angle φ between the voltage and current? (2019)
  • A. 30 degrees
  • B. 60 degrees
  • C. 90 degrees
  • D. 45 degrees
Q. In an AC circuit, if the voltage is given by V(t) = V0 sin(ωt), what is the expression for the current if the circuit is purely inductive? (2023)
  • A. I(t) = I0 sin(ωt)
  • B. I(t) = I0 sin(ωt - π/2)
  • C. I(t) = I0 cos(ωt)
  • D. I(t) = I0 cos(ωt + π/2)
Q. In an AC circuit, if the voltage is given by V(t) = V_0 sin(ωt), what is the expression for the current if the circuit is purely inductive? (2023)
  • A. I(t) = I_0 sin(ωt)
  • B. I(t) = I_0 sin(ωt - π/2)
  • C. I(t) = I_0 cos(ωt)
  • D. I(t) = I_0 cos(ωt + π/2)
Q. In an AC circuit, if the voltage is given by V(t) = V₀ sin(ωt), what is the expression for the current through a capacitor? (2022)
  • A. I(t) = C dV/dt
  • B. I(t) = V₀ sin(ωt)
  • C. I(t) = V₀ cos(ωt)
  • D. I(t) = V₀ sin(ωt)/R
Q. In an AC circuit, the average power consumed is given by which formula? (2022)
  • A. P = VI
  • B. P = VI cos(φ)
  • C. P = V²/R
  • D. P = I²R
Q. In an AC circuit, what is the relationship between the average power and the RMS voltage? (2023)
  • A. P = V_rms²/R
  • B. P = V_peak²/R
  • C. P = V_rms/R
  • D. P = V_peak/R
Q. In an AC circuit, what is the unit of reactance? (2019)
  • A. Ohm
  • B. Farad
  • C. Henry
  • D. Volt
Q. The impedance of an RLC circuit is given by which of the following formulas? (2022)
  • A. Z = R + jX
  • B. Z = √(R² + (X_L - X_C)²)
  • C. Z = R + X_L + X_C
  • D. Z = R - jX
Q. The impedance of an RLC circuit is minimum when which condition is satisfied? (2022)
  • A. XL = XC
  • B. R = 0
  • C. R = XL
  • D. R = XC
Q. What happens to the total current in a parallel RLC circuit at resonance? (2022)
  • A. It is maximum
  • B. It is minimum
  • C. It is zero
  • D. It is constant
Q. What is the average power consumed in an AC circuit with a power factor of 0.5 and an RMS voltage of 100 V with a current of 5 A? (2020)
  • A. 250 W
  • B. 500 W
  • C. 125 W
  • D. 1000 W
Q. What is the average power consumed in an AC circuit with a power factor of 0.8 and a current of 5 A at 230 V? (2022)
  • A. 920 W
  • B. 920 VA
  • C. 1150 W
  • D. 1150 VA
Q. What is the average power consumed in an AC circuit with a power factor of 1? (2019)
  • A. Zero
  • B. RMS voltage
  • C. RMS current
  • D. Maximum power
Q. What is the effect of increasing resistance in a series RLC circuit at resonance? (2023)
  • A. Increases current
  • B. Decreases current
  • C. No effect on current
  • D. Increases voltage
Q. What is the effect of increasing the capacitance in a capacitive AC circuit? (2023)
  • A. Increases current
  • B. Decreases current
  • C. No effect on current
  • D. Increases voltage
Q. What is the effect of increasing the capacitance in an AC circuit? (2019)
  • A. Increases inductive reactance
  • B. Decreases capacitive reactance
  • C. Increases total impedance
  • D. Decreases total current
Q. What is the formula for calculating the average power in an AC circuit? (2023)
  • A. P = VI
  • B. P = VI cos(φ)
  • C. P = V^2/R
  • D. P = I^2R
Q. What is the formula for calculating the impedance in an RLC series circuit? (2022)
  • A. Z = R + jX
  • B. Z = √(R^2 + X^2)
  • C. Z = R + X
  • D. Z = R - jX
Q. What is the peak voltage of an AC source if its RMS voltage is 220 V? (2021)
  • A. 311 V
  • B. 220 V
  • C. 155 V
  • D. 440 V
Q. What is the peak voltage of an AC supply if its RMS voltage is 220 V? (2021)
  • A. 311 V
  • B. 220 V
  • C. 155 V
  • D. 440 V
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