MCQ in Electrical Circuit Part 10 | ECE Board Exam

451. Find the half power bandwidth of a parallel resonant circuit which has a resonant frequency of 3.6 MHz and Q of 218.

A. 606 kHz

B. 58.7 kHz

C. 16.5 kHz

D. 47.3 kHz

452. A current of 10 A and a pf of 0.8 lagging is taken from a single phase 250 V supply. The reactive power of the system is_______.

A. 1500

B. 2000

C. 250

D. not

453.An R-L series ac circuit has 15V across the resistor and 20V across the inductor. The supply voltage is

A. 35 V

B. 5 V

C. 25 V

D. 175 V

454. The active and reactive powers of an inductive circuit are equal. The power factor of the circuit is

A. 0.8 lagging

B. 0.707 lagging

C. 0.6 lagging

D. 0.5 lagging

455. Determine the power angle in the series circuit which consists of R = 25 ohms, L = 0.2 H across a power supply of 200 V, 30 Hz.

A. 36.4 degrees

B. 52.4 degrees

C. 46.4 degrees

D. 56.4 degrees

456. An AC circuit has a resistance of 6 ohms, inductive reactance of 20 ohms, and capacitive reactance of 12 ohms. The circuit power will be

A. 0.8 lagging

B. 0.8 leading

C. 0.6 lagging

D. 0.6 leading

457. A 25 ohm resistor connected in series with a coil of 50 ohm resistance and 150 mH inductance. What is the pf of the circuit?

A. 85%

B. 80%

C. 90%

D. 75%

458. A current wave is represented by the equation i = 10 sin 251t. The average and RMS value of current are

A. 7.07 A; 6.63A

B. 6.36A; 7.07A

C. 10A; 7.07A

D. 6.36A; 10A

459. Calculate the susceptance in mho of a circuit consisting of resistor of 10 ohms in series with a conductor of 0.1 H, when the frequency is 50 Hz.

A. 0.0303

B. 0.0092

C. -0.029

D. 32.95

460. An inductive circuit of resistance 16.5 ohms and inductive of 0.14 H takes a current of 25 A. If the frequency is 50 Hz, the supply voltage is

A. 117.4 V

B. 1174 V

C. 1714 V

D. 1471 V

461. The current taken by a circuit is 1.2 A when the applied potential difference is 250 V and the power taken is 135 W. The power factor is

A. 0.35

B. 0.45

C. 0.55

D. 0.65

462. A capacitor has a capacitance of 20 uF. The current supplied if it is placed across a 1100 V, 25 Hz supply.

A. 3.554 A

B. 6.91 A

C. 3.45 A

D. 9.61 A

463. The form factor of half wave rectified signal is equal to _________.

A. 1.11

B. 0.786

C. 2.22

D. 1.57

464. An impedance draws a current I = 10 cos(wt – 30) from the voltage V = 220sin(wt + 30). What is the impedance?

A. 15.6 – j15.6

B. 15.6 + j15.6

C. 19.1- j11.1

D. 11.0 + j19.1

465. The input of an a.c circuit having pf = 0.8 lagging is 20 KVA. The power drawn by the circuit is ________ Kw.

A. 12

B. 20

C. 16

D. 8

466. A capacitor connected to a 115 V, 25 Hz supply takes 5 A. What current will it take when the capacitance and frequency are doubled?

A. 2 A

B. 5 S

C. 10 A

D. 20 A

467. At what frequency will an inductor of 5mH have the same reactance as a capacitor of 0.1 µF?

A. 7.12 kHz

B. 7.12 Hz

C. 7.12 MHz

D. 7.12 Ghz

468. What capacitance must be placed in series with an inductance of 0.05H, so that when the frequency is 100 Hz, the impedance becomes equal to the ohmic resistance?

A. 70.5 uF

B. 50.7 uF

C. 5.7 uF

D. 7.05 uF

469. A 220 V, 60 Hz source is driving a series R_L circuit. Determine the current in the circuit if R = 100 ohm X_L = 100 ohm.

A. 1.10 lagging

B. 1.55 lagging

C. 2.20 lagging

D. 4.40 lagging

470. What is the resonant frequency of a circuit when an inductance of 1 uH and capacitance of 10 Picofarad are in series?

A. 15.9 MHz

B. 50.3 MHz

C. 15.9 kHz

D. 50.3 KHz

471. The __________ the Q of a circuit, the narrower the bandwidth.

A. Lower

B. Higher

C. Broader

D. Selective

472. A 5 microfarad capacitor is discharged suddenly through a coil having an inductance of 2 H and a resistance of 200 ohms. The capacitor is initially charge to a voltage of 10 volts. Find the additional resistance required just to be prevent oscillation.

A. 1625 ohms

B. 1065 ohms

C. 1265 ohms

D. 1025 ohms

473. The rate of rise of current through an inductive coil is maximum

A. after 1 time constant

B. at the start of current flow

C. near the final maximum value of current

D. at 63.2% of its maximum steady state value

474. A coil of 15 H inductance and 10 ohms resistance is suddenly connected to a 20 volts DC source by closing the switch. The value of current 2 seconds after the switch is closed is

A. 1.74 A

B. 1.47 A

C. 1.17 A

D. 1.71 A

475. A DC voltage of 80 volts is applied to a circuit containing a resistance of 80 ohms in series with an inductance of 20 Henry. Calculate the growth of current at the instant of completing the circuit.

A. 4 A/s

B. 2 A/s

C. ½ A/s

D. ¼ A/s

476. A 200 volt DC supply is suddenly switched to a relay coil which has a time constant of 3 ms. If the current in the coil reaches 0.20 ampere after 3 ms determine the steady state value of the current.

A. 0.361 A

B. 0.163 A

C. 0.316 A

D. 0.631 A

477. A relay has a resistance of 300 ohms and is switched to a 100 V DC supply. If the current reaches 63.2% of its final value at 0.02 sec, determine the inductance of the circuit.

A. 5 H

B. 6 H

C. 4 H

D. 13 H

478. Energy stored by a coil is doubled when its current is increased by ________ percent.

A. 100

B. 141.4

C. 50

D. 25

479. A 60 volt potential difference is suddenly applied to a coil of inductive 60 mH and resistance 180 ohms. At what rate is it rising after 0.005 sec?

A. 322 A/sec

B. 223 A/sec

C. 22.3 A/sec

D. 32.2 A/sec

480. A voltage rise linearly form zero to 100 volts in 1 second, falls instantaneously to zero at t = 1 second and remains zero thereafter. This voltage is applied to an RL series circuit in which R = 5 ohms and L = 100 mH. What is the current when t = 0.50 second?

A. 6.90 A

B. 96 A

C. 9.60 A

D. 69 A

481. A capacitance of 10 microfarad is connected in series with a resistance of 8,000 ohms. If the combination is suddenly connected to a 100 V DC supply. Find the initial rate of rise in potential across the capacitor.

A. 12500 V/s

B. 125 V/s

C. 1250 V/s

D. 12.50 V/s

482. A 25 microfarad capacitor is connected in series with a 0.50 M-ohm resistor and a 120 volt storage battery. What is the potential difference in the capacitor 6 sec after the circuit is closed?

A. 64 volts

B. 46 volts

C. 4.60 volts

D. 6.40 volts

483. A capacitor of 2 microfarad with an initial charge q₀ is connected across the terminals of a 10 ohm resistor and the switch is closed at t = 0. Find q₀ (micro-coulomb) if the transient power in the resistor is known to be P_R = 360^{e-10^(-5)t}

A. 1200

B. 120

C. 102

D. 2100

484. The transient current in a loss-free L-C circuit when excited from an ac source is _________ a/an sine wave .

A. overdamped

B. undamped

C. underdamped

D. critically damped

485. A series RLC circuit with R = 5 ohms, L = 0.10 H, C= 500 microfarad has a constant voltage V = 10 volts applied at t = 0. Find the resulting transient current.

A. 0.707e^-50t sin 139t

B. 0.272e^-25t sin 278t

C. 0.720e^-25t sin 139t

D. none of these

486. A circuit consisting of 20 ohms resistor, 20 mH inductor and a 100 microfarad capacitor in series is connected to a 200 V DC supply. The capacitor is initially uncharged. Find the maximum instantaneous current.

A. 6.45 A

B. 7.45 A

C. 8.45 A

D. 9.45 A

487. A time of 10 ms is required for the current in an RL circuit to reach 90% of its final value. If R is 10 ohms, find the value of C to be inserted in series with the RL circuit so that the frequency of oscillation of the resulting current is 1000 cycles per second.

A. 5.38 x 10^-8 Farad

B. 5.83 x 10^-7 Farad

C. 5.83 x 10^-6 Farad

D. 5.83 x 10^-5 Farad

488. A series RLC circuit with R = 1 kΩ, L = 1 H and C = 6.25 μF is suddenly connected across a 24 V dc source. At t = 0, i= 0 and q = 0. Determine the current after 0.01 sec.

A. 3.45 mA

B. 4.61 mA

C. 5.40 mA

D. 5.05 mA

489. A series RLC circuit has R = 200 Ω, L = 0.1 H and a capacitor C = 10 μF. If a 100 V dc source is connected across the terminals of the series circuit at t = 0, determine the current after 1 millisecond. Assume zero initial conditions.

A. 0.353 A

B. 0.229 A

C. 0.253 A

D. 0.368 A

490. Double energy transient are produced in circuits consisting of

A. two or more resistors

B. resistance and inductance

C. resistance and capacitance

D. resistance, inductance and capacitance

491. A DC voltage source is connected across a series RLC circuit, under steady state conditions, the applied DC voltage drops entirely across the

A. R only

B. L only

C. C only

D. R & L combinations

492. Consider a DC voltage source connected to a series RC circuit. When the steady state reaches, the ratio of energy stored in the capacitor to the total energy supplied by the voltage source is equal to

A. 0.362

B. 0.500

C. 0.632

D. 1.00

493. An inductor at t = 0 with initial current I0 acts as

A. short

B. open

C. current source

D. voltage source

494. An inductor L carries steady state current I0, suddenly at time t = 0 the inductor is removed from circuit and connected to a resistor R. The current through the inductor at time t is equal

A. I₀e^-Rt/L

B. I₀ (1-e^-Rt/L)

C. I₀e^+Rt/L

D. I₀ (1-e^+Rt/L)

495. Transient current in a circuit results from

A. voltage applied to the circuit

B. impedance of the circuit

C. changes in the stored energy in inductors and capacitors

D. resistance of the circuit

496. A two terminal black box contains a single element which can be R, L, C or M. As soon as the box is connected to a dc voltage source, a finite non-zero current is observed to flow through the element. The element is a/an

A. resistance

B. inductance

C. capacitance

D. Mutual inductance

497. In a circuit the voltage across an element is v(t) = 10 (t – 0.01)e^-100t V. The circuit is

A. un-damped

B. under damped

C. critically damped

D. Over damped

498. A unit step voltage is applied at t = 0 to a series RL circuit with zero initial conditions

A. It is possible for the current to be oscillatory

B. The voltage across the resistor at t = 0+ is zero

C. The energy stored in the inductor in the steady state is zero

D. The resistor current eventually falls to zero

499. A 1 µF capacitor charged through a 2 kΩ resistor by a 10 V dc source. The initial growth of capacitor voltage will be at the rate

A. 316 V/ms.

B. 5.0 V/ms

C. 6.32 V/ms

D. 10.0 V/ ms

500. A series R-C circuit has a capacitor with an initial voltage of 11 V. A 15 V dc source is now connected across the R-C circuit. The initial rate of change of capacitor voltage can be

A. 15 Χ 0.368 / RC

B. 15Χ 0.632 / RC

C. 11/RC

D. 4/RC

Questions and Answers in Electrical Circuit

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Complete List of MCQ in Electronics Engineering per topic