AC RMS Phasors AC through R/L/C — Practice Questions

Free NEET Physics multiple-choice questions on AC RMS Phasors AC through R/L/C. Attempt each question and reveal the answer with a full explanation.

An AC voltage V = V 0 t is applied to a purely capacitive circuit. The graph of current I versus t will: Lead the voltage graph by /2 Lag the voltage graph by /2 Be in phase with the voltage graph Lead the voltage graph by If the current in an AC circuit is i = i 0 ( t - /2) and the voltage is V = V 0 t , the power dissipated in the circuit is: Zero V 0 i 0 / 2 V 0 i 0 V 0 i 0 / 2 A 220 V AC supply is connected to a circuit. The peak voltage of this supply is approximately: 311 V 220 V 440 V 155 V A capacitor of capacitance C has a reactance X at frequency f . If both the capacitance and the frequency are doubled, the new reactance will be: X/4 X/2 2X 4X In a purely inductive AC circuit, the current: Lags the voltage by /2 Leads the voltage by /2 Is in phase with the voltage Lags the voltage by The time taken by an AC of 50 Hz to reach its positive peak value from zero is: 5 ms 10 ms 20 ms 2.5 ms In an AC circuit, the frequency is 50 Hz. The instantaneous voltage is V = 100 (100 t) . The time at which the voltage first reaches its maximum value is: 0.005 s 0.01 s 0.02 s 0.0025 s A wattless current is possible in a circuit which contains: Only L or Only C Only R L, C and R R and L Which of the following graphs represents the variation of inductive reactance X L with the frequency f of the AC source? A straight line passing through the origin A parabola A rectangular hyperbola A constant horizontal line In a purely capacitive circuit, the average power dissipated over a complete cycle is: Zero V rms I rms 1/2 C V 0 2 V rms 2 / X C An alternating current of peak value i 0 flows through a resistor R . The rate of heat produced is: 1 2 i 0 2 R i 0 2 R 1 2 i 0 2 R 2 i 0 2 R An inductor of 30 mH is connected to a 220 V, 100 Hz AC source. The inductive reactance is: 6 3 60 1.2 The ratio of the mean value over half a cycle to the peak value of an alternating current is: 2/ /2 1/ 2 / In an AC circuit, the reactance of a capacitor is X C . If the frequency is doubled and the capacitance is halved, then the new reactance will be: X C 2 X C 4 X C X C / 2 Which of the following graphs correctly represents the variation of capacitive reactance X C with frequency f ? A rectangular hyperbola A straight line passing through origin A horizontal straight line A parabola The average power dissipated in a pure inductor connected to an AC source is: Zero 1 2 L I 0 2 V rms I rms V rms I rms ( /4) In an AC circuit, the peak value of voltage is 423 V. Its effective (RMS) voltage is: 300 V 423 V 600 V 211.5 V What is the peak power in an AC circuit with V = V 0 t and I = I 0 ( t - ) ? V 0 I 0 V 0 I 0 2 V 0 I 0 V 0 I 0 2 The power factor of an AC circuit is 0.5 . What is the phase difference between voltage and current? / 3 / 6 / 2 0 The average value of alternating current i = i 0 t over a full cycle is: 0 2i 0 / i 0 / 2 i 0 / 2 An alternating voltage V(t) = 220 2 (100 t) volt is applied to a pure resistance of 110 . The RMS value of current and the frequency of the voltage are respectively: 2 A and 50 Hz 2 2 A and 50 Hz 2 A and 100 Hz 1 A and 50 Hz An alternating current circuit contains only a capacitor. The current in the circuit: Leads the voltage by / 2 Lags the voltage by / 2 Is in phase with the voltage Leads the voltage by An alternating current circuit has resistance R and reactance X . The impedance is Z . The power factor is: R/Z X/Z R/X Z/R An alternating current is given by I = I 0 ( t) . The average value of the current over the first positive half-cycle is: 2I 0 I 0 I 0 2 2I 0 The ratio of peak value and RMS value of an alternating current is: 2 1/ 2 1/2 2 The reactance of a capacitor of capacitance C to a DC (Direct Current) source is: Infinite Zero 1/C May be zero or infinite depending on voltage A capacitor of capacitance C is connected across an AC source of voltage V = V 0 t . The displacement current between the plates of the capacitor would then be given by: I d = V 0 C t I d = V 0 C t I d = V 0 C t I d = V 0 C t The ratio of the magnetic energy density to the electric energy density in an electromagnetic wave in free space is: 1 0 0 0 0 c 2 An alternating current is given by i = i 1 t + i 2 t . The RMS current is given by: 1 2 i 1 2 + i 2 2 1 2 i 1 2 + i 2 2 i 1 + i 2 2 i 1 2 + i 2 2 In an AC circuit, the voltage V and current I are given by V = 100 (100t) V and I = 100 (100t + /3) mA. The power dissipated in the circuit is: 2.5 W 5.0 W 10.0 W 2500 W An inductor L and a resistor R are connected in series to an AC source. If the frequency of the source is increased, the phase angle between the current and the voltage will: Increase Decrease Remain the same First increase then decrease A capacitor of 100 F is connected to a 220 V, 50 Hz AC supply. The RMS value of the current in the circuit is: 6.9 A 11.2 A 3.1 A 0.69 A An AC voltage V = V 0 t is applied to a series R-C circuit. The current in the circuit leads the voltage by a phase angle given by: = 1 RC = RC = R C = L R If the peak value of an AC current is i 0 , then its value at t = /6 is: i 0 / 2 i 0 / 2 i 0 3 / 2 i 0 An inductor of inductance L and resistor of resistance R are joined in series and connected by a source of frequency . The power dissipated in the circuit is: V 2 R / (R 2 + 2 L 2) V 2 R / R 2 + 2 L 2 V R / (R 2 + 2 L 2) V 2 / (R 2 + 2 L 2) In an AC circuit with a resistor R and capacitor C in series, if the frequency of the AC source is decreased, the phase angle by which current leads voltage will: Increase Decrease Remain the same Become zero The average value of the alternating current I = I 0 t over the time interval t=0 to t = / is: 2I 0 / I 0 / I 0 / 2 Zero An inductor of 50 mH is connected to an AC source of 220 V, 50 Hz. The peak current in the circuit is approximately: 19.8 A 14.0 A 22.0 A 7.0 A What is the frequency of an AC voltage that leads to a capacitive reactance of 50 for a 10 F capacitor? 1000/ Hz 500/ Hz 200/ Hz 100/ Hz An alternating current is given by the equation i = i 1 t + i 2 t . The RMS current is given by: 1 2 i 1 2 + i 2 2 i 1 + i 2 2 i 1 2 + i 2 2 1 2 i 1 2 + i 2 2 In a series LCR circuit, if the source frequency is much higher than the resonant frequency, the circuit is: Inductive Capacitive Purely resistive None of these A current is given by i = 3 + 4 t ampere. The RMS value of the current is: 17 A 5 A 7 A 7 2 A If the RMS current in a 50 Hz AC circuit is 5 A, the value of the current 1/300 seconds after its value is zero is: 5 3/2 A 5 2 A 5/2 A 5/ 2 A The RMS value of the current for a triangular wave with peak value I 0 is: I 0 / 3 I 0 / 2 I 0 / 2 2I 0 / In a series AC circuit, the instantaneous voltage is V = V 0 t and the current is I = I 0 t . The average power consumed is: Zero V 0 I 0 / 2 V 0 I 0 V 0 I 0 / 2 The RMS value of a half-wave rectified sinusoidal current with peak value I 0 is: I 0 / 2 I 0 / 2 2I 0 / I 0 / In a purely inductive AC circuit, the instantaneous power P = V I varies with frequency f power . If the supply frequency is f , then f power is: 2f f f/2 Zero The RMS value of the current I = I 0 for 0 < t < T/2 and I = 0 for T/2 < t < T (over one full period T ) is: I 0 / 2 I 0 / 2 I 0 I 0 / In an AC circuit, a resistance R and an inductance L are connected in series. If the frequency of the AC source is changed from to 2 , the new power factor will be (initial phase angle was ): 1 1 + 4 2 1 1 + 2 2 1 2 2 An AC voltage is applied to a resistance R and an inductor L in series. If R and the inductive reactance are both equal to 3 , the phase difference between the applied voltage and the current in the circuit is: /4 /2 Zero /6 In an AC circuit, the current lags the voltage by /4 . The components in the circuit could be: A resistor and an inductor A resistor and a capacitor Only a capacitor Only an inductor A small signal voltage V(t) = V 0 t is applied across an ideal capacitor C . Which of the following is correct? The current I(t) leads voltage V(t) by 90 . The current I(t) lags voltage V(t) by 90 . The current I(t) is in phase with voltage V(t) . The average power dissipated is 1 2 CV 0 2 . The reactance of a capacitor is 10 at a frequency of 50 Hz. If the frequency is increased to 100 Hz, the reactance will be: 5 20 10 2.5