Free Alternating Current MCQs with Answers
592 Alternating Current MCQs from Physics, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Alternating current varies periodically, so phase relationships become essential when current passes through a resistor, capacitor or inductor. The chapter distinguishes resistance from capacitive and inductive reactance, explains phase lead and lag, and connects changing electric and magnetic fields with the production and properties of electromagnetic waves.
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Read the Alternating Current notesFree MDCAT chapter notes with key terms592 questions · page 6 of 30
101. In R.L series circuit with an increase in frequency of A.C source, the impedance of the circuit
- A. increases
- B. remains the same
- C. decreases
- D. may increase or decrease
Explanation: Components of Impedance:The impedance (Z) in an R-L circuit is the total opposition to the flow of AC current and is calculated as:Z =…
Correct answer: increases- A. I leads v by π/2
- B. I and v are in phase
- C. I lags V by π/2
- D. None
Explanation: Capacitive Reactance:In an AC circuit, a capacitor offers opposition to current flow through the property of capacitive reactance (XC)…
Correct answer: I leads v by π/2- A. P = VI
- B. P=VIcos
- C. P=VIsin(θ)
- D. P=VItan(θ)
Explanation: In an AC circuit, the real power (P) is given by the product of voltage (V), current (I), and the power factor (cosine of the phase angle…
Correct answer: P=VIcos- A. √2V
- B. √5 V
- C. √3V
- D. √7V
Explanation: In a three-phase AC supply, the phase voltage (V) is the voltage between any one of the live wires and the neutral wire.
Correct answer: √3V- A. 0
- B. Constant
- C. +ive
- D. Max
Explanation: In an alternating current (AC) circuit, the flow of electric current periodically changes direction.
Correct answer: 0- A. Any angle between 0 and ±π/2
- B. π/2
- C. π
- D. Any angle between 0 and π/2
Explanation: In an LCR (inductor, capacitor, resistor) series AC circuit, the phase angle between current and voltage depends on the values of…
Correct answer: Any angle between 0 and π/2- A. resistive circuit
- B. capacitive circuit
- C. inductive circuit
- D. resonant circuit
Explanation: In an RLC series circuit, when the frequency of the AC source is very low, the circuit behaves like a capacitor-dominated circuit, also…
Correct answer: capacitive circuit- A. V leads q
- B. V legs q
- C. V and q are in phase
- D. none of these
Explanation: In an AC circuit with a capacitor, the relationship between voltage (V) and charge (Q) is as follows:a.
Correct answer: V leads q- A. 0
- B. 90
- C. 180
- D. 270
Explanation: In an RLC series resonance circuit, at resonance, the phase angle between the voltage and current equals:a.
Correct answer: 0- A. 0
- B. Constant
- C. +
- D. max:
Explanation: The average value of current in an AC cycle is equal to the maximum current (amplitude) divided by the square root of 2.In summary, option…
Correct answer: max:111. The inductive reactance of the coil having inductance of 0.5 henry in which AC of 50 Hz flows is
- A. 94.2 ohm
- B. 1.57 ohm
- C. 157 ohm
- D. 9.4 ohm
Explanation: The inductive reactance of a coil is given by \(X_L = 2πfL\), where \(f\) is the frequency of the AC and \(L\) is the inductance of the…
Correct answer: 157 ohm- A. Resistive circuit
- B. Capacitive circuit
- C. Inductive circuit
- D. Resonant circuit
Explanation: When the frequency of the AC source is very low, the inductive reactance (\(X_L\)) and capacitive reactance (\(X_C\)) in the circuit…
Correct answer: Resistive circuit- A. First law of thermodynamics
- B. Second law of thermodynamics
- C. Third law of thermodynamics
- D. None of these
Explanation: The second law of thermodynamics states that in any energy transfer or transformation, there will always be an increase in the entropy of…
Correct answer: Second law of thermodynamics- A. Rectification
- B. Amplification
- C. Modulation
- D. Magnification
Explanation: Modulation is the process of varying the characteristics of a carrier wave (high-frequency signal) in proportion to the information signal…
Correct answer: Modulation- A. One time
- B. Two times
- C. Four times
- D. A number of times depending on the frequency
Explanation: An alternating voltage sine wave consists of a positive half-cycle and a negative half-cycle.
Correct answer: Two times- A. X rays
- B. Gamma rays
- C. None of these
- D. Beta rays
Explanation: X-rays and gamma rays are electromagnetic waves, so they can travel in a vacuum.
Correct answer: None of these- A. Leads the voltage by 90° or π/2
- B. Lags behind voltage by 90° or π/2
- C. Is in phase with voltage
- D. None of the above
Explanation: In a purely capacitive AC circuit, the current must flow to charge the capacitor plates before a voltage can build up across them.
Correct answer: Leads the voltage by 90° or π/2- A. Increases
- B. Decreases
- C. Remains the same
- D. Increases only when the voltage increases
Explanation: Capacitive reactance is given by the formula Xc = 1 / (2πfC). This shows that reactance is inversely proportional to the frequency (f).
Correct answer: Decreases- A. 60°
- B. 45°
- C. 30°
- D. 90°
Explanation: The RMS value is I (rms) = I (peak) / √2. The instantaneous current is I (inst) = I (peak) sin(θ).
Correct answer: 45°- A. Voltage
- B. Current
- C. Impedance
- D. Reactance
Explanation: 1 MWh = 10 W × 3600 s = 3.6×10 J = 3.6 GJ. Thus option D is the correct conversion.
Correct answer: Reactance