Alternating Current PYQs Set 1 (PDF)

Set 1 of 9 · Questions 1-30 of 244

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Mere Teacher · Previous Year Questions NEET Physics · Alternating Current · Set 1 (Q1-30)
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1. $An alternating current is represented by the equation, i = 1002 sin (100 πt) ampere. The RMS value of current and the frequency of the given alternating current are$ (1) $\frac{100}{2} A, 100 Hz$ (2) $502 A, 50 Hz$ (3) $1002 A, 100 Hz$ (4) $100 A, 50 Hz$ 2. $A series LCR circuit is connected to an ac source of voltage 150 sin (80 πt) volt. If the resistance of the resistor in the circuit is 25Ω and the impedance in the circuit is 75Ω, the average power dissipated per cycle in the circuit is$ (1) $75 W$ (2) $200 W$ (3) $50 W$ (4) $100 W$ 3. $If wattless current flows in the AC circuit, then the circuit is$ (1) $Purely Resistive circuit$ (2) $Purely Inductive circuit$ (3) $LCR series circuit$ (4) $RC series circuit only$ 4. $The frequency of ac at which 16 μF capacitor and \frac{10}{π ^{2}} mH inductor will have same reactance is$ (1) $1 kHz$ (2) $1.25 kHz$ (3) $1.5 kHz$ (4) $2 kHz$ 5. $In an oscillating LC circuit, L = 3.00 mH and C = 2.70 μF . At t = 0, the charge on the capacitor is zero and the current is 2.00 A . The maximum charge that will appear on the capacitor will be$ (1) $1.8 \times 10^{- 5} C$ (2) $18 \times 10^{- 5} C$ (3) $9 \times 10^{- 5} C$ (4) $90 \times 10^{- 5} C$ 6. $A circuit element X when connected to an a.c. supply of peak voltage 100 V gives a peak current of 5 A which is in phase with the voltage. A second element Y when connected to the same a.c. supply also gives the same value of peak current which lags behind the voltage by \frac{π}{2} . If X and Y are connected in series to the same supply, what will be the rms value of the current in ampere?$ (1) $\frac{10}{2}$ (2) $\frac{5}{2}$ (3) $52$ (4) $\frac{5}{2}$ 7. $The power factor of an AC circuit containing peak current 2 A and peak voltage 1 V is 1/2, then the angle between voltage and current is$ (1) $30^{\circ}$ (2) $45^{\circ}$ (3) $90^{\circ}$ (4) $60^{\circ}$ 8. $For a transformer, the turns ratio is 3 and its efficiency is 0.75 . The current flowing in the primary coil is 2 A and the voltage applied to it is 100 V . Then the voltage and the current flowing in the secondary coil are respectively.$ (1) $150 V, 1.5 A$ (2) $300 V, 0.5 A$ (3) $300 V, 1.5 A$ (4) $150 V, 0.5 A$ 9. $A 100 W bulb is connected to an AC source of 220 V, 50 Hz . Then the current flowing through the bulb is$ (1) $\frac{5}{11} A$ (2) $1 2 A$ (3) $2 A$ (4) $\frac{3}{4} A$ 10. $When you walk through a metal detector carrying a metal object in your pocket, it raises an alarm. This phenomenon works on$ (1) $Electromagnetic induction$ (2) $Resonance in ac circuits$ (3) $Mutual induction in ac circuits$ (4) $interference of electromagnetic waves$ 11. $In a series LR circuit with X_{L} = R. power factor is pi. If a capacitor of capacitance C with X_{c} = X_{L} is added to the circuit the power factor becomes P_{2} . The ratio of P_{1} to P_{2} will be:$ (1) $1 : 3$ (2) $1 : 2$ (3) $1 : 1$ (4) $1 : 2$ 12. $In LC parallel resonance circuit, choose the wrong statement.$ (1) $At resonance, current is minimum.$ (2) $At resonance, impedance is maximum.$ (3) $Resonance occurs when inductive and capacitive reactance is same.$ (4) $At resonance, resonant frequency = LC .$ 13. $An alternating emf E = 440 sin100 π t is applited to a circuit containing an inductance of \frac{2}{π} H. If an a.c. ammeter is connected in the circuit, its reading will be:$ (1) $4.4 A$ (2) $1.55 A$ (3) $2.2A$ (4) $3.11 A$ 14. $In a series LR circuit XL = R and power factor of the circuit is P_{l} . When capacitor with capacitance C such that XL = X_{c} is put in series, the power factor becomes P_{2} . The ratio \frac{P _{1}}{P _{2}} is$ (1) $\frac{1}{2}$ (2) $\frac{1}{2}$ (3) $\frac{3}{2}$ (4) $2 : 1$ 15. $A power transmission line feeds input power at 2300 V to a step down transformer with its primary windings having 4000 turns. The output power is delivered at 230 V by the transformer. If the current in the primary of the transformer is 5A and its efficiency is 90%, the output current would be:$ (1) $45 A$ (2) $25 A$ (3) $35 A$ (4) $50 A$ 16. $A capacitance of (\frac{10 ^{- 3}}{2 π}) F and an inductance of (\frac{100}{π}) mH and a resistance of 10Ω are connected in series with an AC voltage source of 220 V, 50 Hz . The phase angle of the circuit is$ (1) $60^{\circ}$ (2) $30^{\circ}$ (3) $45^{\circ}$ (4) $90^{\circ}$ 17. $A capacitor of capacitance 150.0 μ F is connected to an alternating source of emf given by E = 36 sin(120 π) V. The maximum value of current in the circuit is approximately equal to:$ (1) $2 A$ (2) $2 A$ (3) $22 A$ (4) $\frac{1}{2} A$ 18. $A 100Ω resistance, a 0.1 μF capacitor and an inductor are connected in series across a 250V supply at variable frequency. Calculate the value of inductance of inductor at which resonance will occur. Given that the resonant frequency is 60 Hz .$ (1) $0.70H$ (2) $70.3mH$ (3) $7.03 \times 1 0^{- 5} H$ (4) $70.3H$ 19. $In a LCR series circuit, the potential difference between the terminals of the inductance is 60 V, between the terminals of the capacitor is 30 V and that across the resistance is 40 V . Then, supply voltage will be equal to$ (1) $50 V$ (2) $70 V$ (3) $130 V$ (4) $10 V$ 20. $An inductor coil stores 64 J of magnetic field energy and dissipates energy at the rate 640 W of when a current 8 A of is passed through it. If this coil is joined across an ideal battery, find the time constant of the circuit in seconds:$ (1) $0.4$ (2) $0.8$ (3) $0.125$ (4) $0.2$ 21. $A circular coil of area 0.01 m^{2} and 40 turns is rotated about its vertical diameter with an angular speed of 50 rad s^{- 1} in a uniform horizontal magnetic field 0.05 T . If the average power loss due to joule heating is 25 mW, then the closed loop resistance of the coil is$ (1) $50Ω$ (2) $12.5Ω$ (3) $75Ω$ (4) $20Ω$ 22. $An AC circuit has R = 100Ω, C = 2 μF and L = 80 mH, connected in series. The quality factor for the circuit is$ (1) $20$ (2) $2$ (3) $0.5$ (4) $400$ 23. $In an ac circuit, the instantaneous current is zero, when the instantaneous voltage is maximum. In this case, the source may be connected to: (A) pure inductor.(B) pure capacitor.(C) pure resistor.(D) combination of an inductor and capacitor. Choose the correct answer from the options given below:$ (1) $A, B and C only$ (2) $A and B only$ (3) $B, C and D only$ (4) $A, B and D only$ 24. $The potential differences across the resistance, capacitance and inductance are 80 V, 40 V and 100 V respectively in an L - C - R circuit. The power factor of this circuit is [NEET 2016]$ (1) $0.4$ (2) $0.5$ (3) $0.8$ (4) $1.0$ 25. $An inductor and a resistor are connected in series to an ac source. If the power factor of the circuit is 0.5 , the ratio of the resistance of the resistor and the reactance of the inductor is$ (1) $1 : 1$ (2) $1 : 2$ (3) $1 : 3$ (4) $1 : 2$ 26. $A resistor of resistance 40Ω, a capacitor of capacitive 20Ω and an inductor of inductive reactance 50Ω are connected in series to an ac source of 100 V . The current through the circuit is$ (1) $0.5 A$ (2) $1 A$ (3) $1.5 A$ (4) $2 A$ 27. $The equation of current in a purely inductive circuit is 5 sin(49 π -30°). If the inductance is 30 mH then the equation for the voltage across the inductor, will be: (Let π = \frac{22}{7})$ (1) $147sin(49 π t - 30°)$ (2) $1.47sin(49 π t + 60°)$ (3) $23.1sin(49 π t - 30°)$ (4) $23.1sin(49 π t + 60°)$ 28. $A series combination of resistor (R), capacitor (C) is connected to an A.C. source of angular frequency ' ω'. Keeping the voltage same, if the frequency is changed to \frac{ω}{3}, the current becomes half of the original current. Then the ratio of the capacitive reactance and resistance at the former frequency is$ (1) $0.6$ (2) $3$ (3) $2$ (4) $6$ 29. $A coil is suspended in a uniform magnetic field, with the plane of the coil parallel to the magnetic lines of force. When a current is passed through the coil it starts oscillating; it is very difficult to stop. But if an aluminium plate is placed near to the coil, it stops. This is due to:$ (1) $developement of air current when the plate is placed.$ (2) $induction of electrical charge on the plate$ (3) $shielding of magnetic lines of force as aluminium is a paramagnetic material.$ (4) $Electromagnetic induction in the aluminium plate giving rise to electromagnetic damping.$ 30. $An ideal transformer has a turns ratio of 10 . When the primary is connected to 220 V, 50 Hz ac source, the power output is$ (1) $10 times the power input$ (2) $\frac{1}{10} th the power input$ (3) $equal to power input$ (4) $zero$