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
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Solution
The time period (T) is the reciprocal of frequency (f). Therefore, T = 1/f = 1/50 Hz = 0.02 s.
Correct Answer: A — 0.02 s
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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
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Solution
Inductive reactance (X_L) is directly proportional to frequency (f). Therefore, if frequency increases, X_L decreases.
Correct Answer: B — Decreases
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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
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Solution
Inductive reactance (X_L) is given by X_L = 2πfL. If the inductance (L) is doubled, X_L will also double.
Correct Answer: A — It doubles
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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
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Solution
The peak voltage (V_peak) is calculated as V_peak = V_rms × √2 = 100 V × √2 ≈ 141.42 V.
Correct Answer: B — 141.42 V
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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
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Solution
Inductive reactance (X_L) is given by X_L = V/I. Here, X_L = 100 V / 2 A = 50 Ω.
Correct Answer: A — 50 Ω
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Q. In a series RLC circuit, at resonance, the impedance is equal to which of the following? (2020)
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Solution
At resonance in a series RLC circuit, the impedance (Z) is equal to the resistance (R) because the inductive and capacitive reactances cancel each other out.
Correct Answer: B — R
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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
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Solution
At resonance in a series RLC circuit, the impedance is minimum, and the circuit behaves like a purely resistive circuit.
Correct Answer: A — Impedance is minimum
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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
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Solution
At resonance in a series RLC circuit, the impedance is minimum, and thus the current is maximum.
Correct Answer: A — It is maximum
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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
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Solution
At resonance in a series RLC circuit, the total impedance is minimum and is equal to the resistance (R) of the circuit.
Correct Answer: C — It is equal to R
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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
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Solution
The power factor (PF) is given by cos(θ). If θ = 30 degrees, PF = cos(30°) = √3/2 ≈ 0.866.
Correct Answer: A — 0.866
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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
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Solution
The power factor (cosφ) is 0.5, which corresponds to an angle φ of 60 degrees.
Correct Answer: B — 60 degrees
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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)
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Solution
In a purely inductive circuit, the current lags the voltage by 90 degrees (π/2 radians). Therefore, I(t) = I0 sin(ωt - π/2).
Correct Answer: B — I(t) = I0 sin(ωt - π/2)
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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)
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Solution
In a purely inductive circuit, the current lags the voltage by 90 degrees (or π/2 radians). Therefore, I(t) = I_0 sin(ωt - π/2).
Correct Answer: B — I(t) = I_0 sin(ωt - π/2)
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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
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Solution
The current through a capacitor is given by I(t) = C dV/dt. For V(t) = V₀ sin(ωt), the current can be derived from this expression.
Correct Answer: A — I(t) = C dV/dt
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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
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Solution
The average power (P) consumed in an AC circuit is given by P = VI cos(φ), where φ is the phase angle between voltage and current.
Correct Answer: B — P = VI cos(φ)
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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
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Solution
The average power (P) in an AC circuit is given by P = V_rms²/R, where R is the resistance.
Correct Answer: A — P = V_rms²/R
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Q. In an AC circuit, what is the unit of reactance? (2019)
A.
Ohm
B.
Farad
C.
Henry
D.
Volt
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Solution
Reactance is measured in Ohms, just like resistance.
Correct Answer: A — Ohm
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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
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Solution
The impedance (Z) of an RLC circuit is given by Z = √(R² + (X_L - X_C)²), where X_L is the inductive reactance and X_C is the capacitive reactance.
Correct Answer: B — Z = √(R² + (X_L - X_C)²)
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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
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Solution
The impedance (Z) of an RLC circuit is minimum when the inductive reactance (X_L) equals the capacitive reactance (X_C), which is the condition for resonance.
Correct Answer: A — XL = XC
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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
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Solution
At resonance in a parallel RLC circuit, the total current is maximum because the impedance is at its minimum.
Correct Answer: A — It is maximum
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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
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Solution
Average power (P) is given by P = V_rms × I_rms × power factor. Thus, P = 100 V × 5 A × 0.5 = 250 W.
Correct Answer: A — 250 W
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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
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Solution
Average power (P) is given by P = V × I × PF. Here, P = 230 V × 5 A × 0.8 = 920 W.
Correct Answer: A — 920 W
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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
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Solution
When the power factor is 1, the average power consumed is maximum and is given by P = V_rms × I_rms.
Correct Answer: D — Maximum power
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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
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Solution
Increasing resistance in a series RLC circuit at resonance will decrease the current, as the impedance increases.
Correct Answer: B — Decreases current
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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
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Solution
In a capacitive AC circuit, increasing the capacitance decreases the capacitive reactance (X_C), which increases the current (I = V/X_C).
Correct Answer: A — Increases current
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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
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Solution
Increasing the capacitance decreases the capacitive reactance (X_C = 1/(2πfC)), which can lead to an increase in current.
Correct Answer: B — Decreases capacitive reactance
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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
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Solution
The average power (P) in an AC circuit is given by P = VI cos(φ), where φ is the phase difference between voltage and current.
Correct Answer: B — P = VI cos(φ)
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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
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Solution
The impedance (Z) in an RLC series circuit is calculated using the formula Z = √(R^2 + X^2), where X is the total reactance.
Correct Answer: B — Z = √(R^2 + X^2)
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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
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Solution
The peak voltage (V_peak) is related to the RMS voltage (V_rms) by the formula V_peak = V_rms × √2. Therefore, V_peak = 220 V × √2 ≈ 311 V.
Correct Answer: A — 311 V
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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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Solution
The peak voltage (V_peak) is related to the RMS voltage (V_rms) by the formula V_peak = V_rms × √2. Therefore, V_peak = 220 V × √2 ≈ 311 V.
Correct Answer: A — 311 V
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