MCQOPTIONS
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MCQOPTIONS
This section includes 49 Mcqs, each offering curated multiple-choice questions to sharpen your Network Theory knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
A load of three impedances each (6 + j9) is supplied through a line having an impedance of (1 + j2) Ω. The supply voltage is 400 V at 50 Hz. Determine input and output powers respectively when the load is star connected. |
| A. | 5469 W and 6591 W |
| B. | 4359 W and 8269 W |
| C. | 6591 W and 5649 W |
| D. | 6688 W and 9854 W |
| Answer» D. 6688 W and 9854 W | |
| 2. |
In balanced three-phase star-connected sources, the angle are \(\angle \left( {\overline V_a,\overline V_{ab}} \right)\), \(\angle \left( {\overline V_b,\overline V_{bc}} \right)\), \(\angle \left( {\overline V_c,\overline V_{ca}} \right)\) |
| A. | All equal to -30° |
| B. | All equal to +30° |
| C. | All equal to +90° |
| D. | All equal to -90° |
| Answer» B. All equal to +30° | |
| 3. |
For a star-connected three-phase AC circuit, the: |
| A. | line current is equal to three times the phase current |
| B. | phase current is equal to the line current |
| C. | phase current is three times the line current |
| D. | line current is equal to the phase voltage |
| Answer» C. phase current is three times the line current | |
| 4. |
Line current of 3 phase delta connection |
| A. | is equal to phase current |
| B. | is 1/√ 3 times the phase current |
| C. | is √3 times the phase current |
| D. | none of the above |
| Answer» D. none of the above | |
| 5. |
In a balanced three-phase star connected system, if the line current is 30 A, then its phase current is: |
| A. | 15 A |
| B. | 17.3 A |
| C. | 30 A |
| D. | 51.9 A |
| Answer» D. 51.9 A | |
| 6. |
\({\overline V _a}\) = 1∠0°, \({\overline V _b}\) = 1∠120°, \({\overline V _c}\) = 1∠240° constitute a balanced set of three phase voltages. The magnitude and angle of voltage \(\overline V_{bc}\) are |
| A. | 1/√3, -90° |
| B. | √3, +90° |
| C. | √3, -30° |
| D. | 1/√3, +30° |
| Answer» C. √3, -30° | |
| 7. |
If a system is connected in delta connection, how can be the total power output expressed as? |
| A. | \(\frac{1}{{\sqrt {3{V_P}{I_P}\sin \phi } }}\) |
| B. | \(\sqrt {3{V_P}{I_P}} \cos \phi \) |
| C. | \(\frac{1}{3}{V_P}{I_P}\cos \phi\) |
| D. | \(3{V_P}{I_P}\cos \phi\) |
| Answer» E. | |
| 8. |
In a three-phase system, the relation IL = √3Iph is applicable to a: |
| A. | single-phase system too |
| B. | delta-connected load |
| C. | star-connected load without a neutral point |
| D. | star-connected load |
| Answer» C. star-connected load without a neutral point | |
| 9. |
In star connection, if the phase voltage is 1732 V then what will be the line voltage? |
| A. | 1500 V |
| B. | 3000 V |
| C. | 1732 V |
| D. | 1000 V |
| Answer» C. 1732 V | |
| 10. |
A balanced star connected a load of (8 + j6) Ω per phase is connected to a balanced 3-phase 400 V supply. Find the power factor |
| A. | 0.8 lead |
| B. | 0.8 lag |
| C. | 1 |
| D. | 0.6 lag |
| Answer» C. 1 | |
| 11. |
A three-phase star-connected balanced load of (4 + j3) Ω per phase is connected across a three-phase, 50 Hz, 400 V AC supply. Determine the power factor of the load. |
| A. | 0.8 lagging |
| B. | 0.3 leading |
| C. | 0.9 lagging |
| D. | 0.7 leading |
| Answer» B. 0.3 leading | |
| 12. |
For a 3-phase load balanced condition, each phase has the same value of ______. |
| A. | Impedance |
| B. | Resistance |
| C. | Power factor |
| D. | All options are correct |
| Answer» E. | |
| 13. |
In delta connection, the relation between line current and phase current is ______. |
| A. | \({I_L} = \frac{{{I_{ph}}}}{{\sqrt 3 }}\) |
| B. | IL = Iph |
| C. | IL = √3 Iph |
| D. | IL = 3Iph |
| Answer» D. IL = 3Iph | |
| 14. |
Line voltage in star connected balanced 3 phase circuit |
| A. | is equal to phase voltage |
| B. | is 1/√3 times the phase voltage |
| C. | is √3 times the phase voltage |
| D. | none of the above |
| Answer» D. none of the above | |
| 15. |
A three-phase balanced, the delta-connected load of (4 + j8) Ω is connected to a 400-V, 3-ϕ balanced power supply. Assuming that the phase sequence is RYB, determine the phase current IR. |
| A. | 45.74 ∠ -63.4° A |
| B. | 44.74 ∠ -63.4° A |
| C. | 44.74 ∠ 63.4° A |
| D. | 45.74 ∠ 63.4° A |
| Answer» C. 44.74 ∠ 63.4° A | |
| 16. |
In a three-phase system, the order in which the voltages attain their maximum positive value is called ________. |
| A. | RMS voltage |
| B. | peak-to-peak voltage |
| C. | a phase sequence |
| D. | power factor |
| Answer» D. power factor | |
| 17. |
A 3 – phase load of 0.8 pf lag is supplied from a balanced 3 – phase supply of phase sequence RYB. with VYB as reference the current IR will |
| A. | In phase with V |
| B. | Lag VYB by 36.76° |
| C. | lead VYB by 53.24° |
| D. | lag VYB by 53.24° |
| Answer» D. lag VYB by 53.24° | |
| 18. |
In a balanced 3 phase 4 wire system of power transmission, the phase sequence is RYB. If the voltage of R phase is 400∠0° volts. Then the voltage of B phase is: |
| A. | 400 ∠-240° V |
| B. | 400 ∠240° V |
| C. | 400 ∠0° V |
| D. | 400 ∠-120° V |
| Answer» B. 400 ∠240° V | |
| 19. |
A three-phase power system with three voltages EA, EB and EC have an equal magnitude and are displaced at ____ from each other. |
| A. | 100° |
| B. | 180° |
| C. | 90° |
| D. | 120° |
| Answer» E. | |
| 20. |
For the three-phase circuit shown in the figure the ratio of the currents IR: IY:IB is given by |
| A. | \(1\;:\;1\; :\sqrt 3 \) |
| B. | 1 : 1 : 2 |
| C. | 1 : 1 : 0 |
| D. | \(1:1:\sqrt {3/2} \) |
| Answer» B. 1 : 1 : 2 | |
| 21. |
Find the phase current if a three-phase star-connected system is connected to a 400 V, 50 Hz AC supply. Assume Zph consists of a resistance of 10 Ω in series with an inductance of 0.0318 H. |
| A. | 2.30 A |
| B. | 40 A |
| C. | 23.23 A |
| D. | 16.33 A |
| Answer» E. | |
| 22. |
Find the phase voltage if a three-phase star-connected system is connected to a 400 V, 50 Hz AC supply. Assume Zph Consists of resistance of 10 Ω in series with an inductance of 0.0318 H. |
| A. | 400 V |
| B. | 230.94 V |
| C. | 230 V |
| D. | 110.24 V |
| Answer» C. 230 V | |
| 23. |
In a balanced three-phase, star-connected system, the phase difference between phase voltages and their respective line voltages is: |
| A. | 30° |
| B. | 60° |
| C. | 120° |
| D. | 45° |
| Answer» B. 60° | |
| 24. |
A three-phase motor connected with a 400 V balanced system consumes 1732 watts at a power factor of 0.5. The line current will be: |
| A. | 10 A |
| B. | 25 A |
| C. | 8.66 A |
| D. | 5 A |
| Answer» E. | |
| 25. |
In a 3-Phase star connected system, the line current is |
| A. | equal to phase current |
| B. | 1/√3 times phase current |
| C. | √3 times phase current |
| D. | 3 times phase current |
| Answer» B. 1/√3 times phase current | |
| 26. |
Delta/star or star/delta transformation technique is applied to |
| A. | one terminal network |
| B. | two terminal network |
| C. | three terminal network |
| D. | none of these |
| Answer» D. none of these | |
| 27. |
Apparent power in three phase star connected balanced load is given by |
| A. | √3 VLIL |
| B. | √3 VLIL cos ϕ |
| C. | √3 VLIL sin ϕ |
| D. | None of the above |
| Answer» B. √3 VLIL cos ϕ | |
| 28. |
For a 400 V, 3 phase 3 wire star-connected unbalanced load, the neutral point voltage can be: |
| A. | 400 V |
| B. | Zero |
| C. | 20 V |
| D. | 800 V |
| Answer» D. 800 V | |
| 29. |
Find the phase current if a three-phase star-connected system is connected to a 400 V, 50 Hz AC supply. Assume Zph = (9.8 + j10) Ω |
| A. | 28.57 A |
| B. | 10 A |
| C. | 11.44 A |
| D. | 16.5 A |
| Answer» E. | |
| 30. |
A three-phase star-connected balanced load of (4 + j3) Ω per phase is connected across a three-phase, 50 Hz, 400 V AC supply. Determine current drawn from the supply |
| A. | 46.188 A |
| B. | 20.23 A |
| C. | 50.54 A |
| D. | 50.522 A |
| Answer» B. 20.23 A | |
| 31. |
A source is supplying a load through a 2-phase, 3-wire transmission system as shown in figure below. The instantaneous voltage and current in phase-a are \({V_{an}} = 220\sin \left( {100\pi t} \right)V\) and \({i_a} = 10\sin \left( {100\pi t} \right)A\) respectively. Similarly, for phase-b, the instantaneous voltage and current are \({V_{bn}} = 220\cos \left( {100\pi t} \right)V\) and \({i_b} = 10\cos \left( {100\pi t} \right)A\) respectively.The total instantaneous power flowing from the source to the load is |
| A. | 2200 W |
| B. | 2200 sin2(100πt) W |
| C. | 4400 W |
| D. | 2200 sin(100πt)cos(100πt) W |
| Answer» B. 2200 sin2(100πt) W | |
| 32. |
Find the power factor for the given circuit. |
| A. | 0.8 lagging |
| B. | 0.6 leading |
| C. | 0.75 lagging |
| D. | 0.6 lagging |
| Answer» E. | |
| 33. |
A balanced delta-connected load (16 + j12)Ω/phase is connected to a 3-phase 230 V balanced supply. The line current and the real power drawn respectively are |
| A. | 19.9 A and 3.17 kW |
| B. | 11.5 A and 6.34 kW |
| C. | 19.9 A and 6.34 kW |
| D. | 11.5 A and 3.17 kW |
| Answer» D. 11.5 A and 3.17 kW | |
| 34. |
In a three-phase load, ______ different impedances are connected together in a star or delta fashion. |
| A. | six |
| B. | zero |
| C. | three |
| D. | one |
| Answer» D. one | |
| 35. |
In a three phase supply, the phase angle between the phases are: |
| A. | 120° & 240° |
| B. | 90° & 180° |
| C. | 90° & 270° |
| D. | 180° & 270° |
| Answer» B. 90° & 180° | |
| 36. |
In a three-phase system, the relation IL = Iph is applicable to a ________. |
| A. | delta-connected load |
| B. | star-connected load without neutral point |
| C. | single-phase system |
| D. | star-connected load |
| Answer» E. | |
| 37. |
In a balanced star connected system, line voltages are ________ ahead of their respective phase voltages. |
| A. | 60° |
| B. | 30° |
| C. | 240° |
| D. | 120° |
| Answer» C. 240° | |
| 38. |
In a delta connection, if the magnitude of phase voltage is Vp and the magnitude of phase current is Ip, then the expression for the complex power is:Assume load to be capacitive |
| A. | \({S^*} = \sqrt 3 {V_P}{I_P}\angle \phi \;VA\) |
| B. | \({S^*} = \sqrt 3 {V_P}{I_P}\angle - \phi \;VA\) |
| C. | \({S^*} = {V_P}{I_P}\;\angle \phi \;VA\) |
| D. | \({S^*} = 3{V_P}{I_{P\;}}\angle - \phi \;VA\) |
| Answer» E. | |
| 39. |
In a delta connection, line current lags behind phase current by: |
| A. | 30° |
| B. | 60° |
| C. | 90° |
| D. | 120° |
| Answer» B. 60° | |
| 40. |
Find the phase voltage if a three-phase star-connected system is connected to a 400 V, 50 Hz AC supply. Assume Zph = (9.8 + j10) Ω |
| A. | 110.24 V |
| B. | 230.94 V |
| C. | 400 V |
| D. | 230 V |
| Answer» C. 400 V | |
| 41. |
A balanced 3 phase star connected voltage source having positive sequence RYB with\(\overrightarrow {{E}}_{RY} = 10\angle 0^\circ V\) is applied to a balanced delta connected load having \(5\angle 30^\circ \Omega\) impedance per phase. The line current \(\bar{l}_n\) drawn by the load is |
| A. | \(\frac{2}{{\sqrt 3 }}\angle 60^\circ A\) |
| B. | \(\frac{2}{{\sqrt 3 }}\angle - 30^\circ A\) |
| C. | \(\frac{2}{{\sqrt 3 }}\angle - 60^\circ A\) |
| D. | \({2}{{\sqrt 3 }}\angle - 60^\circ A\) |
| Answer» E. | |
| 42. |
In a three-phase system, the current passing through any two lines of supply is called ________. |
| A. | line voltage |
| B. | phase current |
| C. | phase voltage |
| D. | line current |
| Answer» E. | |
| 43. |
In a three-phase system, the relation VL = Vph is applicable to a ________. |
| A. | star-connected load |
| B. | delta-connected load |
| C. | star-connected without a neutral point |
| D. | single-phase system also |
| Answer» C. star-connected without a neutral point | |
| 44. |
A Y connected load is supplied from 3-phase 240 V mains. Each branch of the load is a resistor of 20 Ω. Using 240 V and 10 kVA, calculate the values of the current and power taken by the load. |
| A. | 6.9 A, 2.88 kW |
| B. | 2.9 A, 6.88 kW |
| C. | 4.5 A, 3.7 kW |
| D. | 8.9 A, 4.88 kW |
| Answer» B. 2.9 A, 6.88 kW | |
| 45. |
Let V be the phase voltage of a three-phase, four-wire distribution system. What could be the line voltage of the system? |
| A. | √3 × V |
| B. | V/3 |
| C. | V/√2 |
| D. | V/√3 |
| Answer» B. V/3 | |
| 46. |
Find the line current if a three-phase star-connected system is connected to a 400 V, 50 Hz AC supply. Assume Zph = (9.8 + j10) Ω |
| A. | 28.57 A |
| B. | 16.5 A |
| C. | 10 A |
| D. | 11.44 A |
| Answer» C. 10 A | |
| 47. |
Consider a three-phase system and match the following:A. Active powerD. \(\sqrt 3\) VLILB. Reactive powerE. \(\sqrt 3\) VLIL sin ϕC. Apparent powerF. \(\sqrt 3\) VLIL cos ϕ |
| A. | A-F, B-D, C-E |
| B. | A-F, B-E, C-D |
| C. | A-E, B-F, C-D |
| D. | A-D, B-F, C-E |
| Answer» C. A-E, B-F, C-D | |
| 48. |
A balanced RYB-sequence, Y-connected (star connected) source with VRN = 100 volts is connected to a Δ-connected (delta connected) balanced load of (8 + j6) ohms per phase. Then the phase current and line current values respectively, are |
| A. | 10 A, 30 A |
| B. | 10√3 A, 30 A |
| C. | 10 A, 10 A |
| D. | 10√3 A, 10√3 A |
| Answer» C. 10 A, 10 A | |
| 49. |
In delta connected circuit, when one resistor is open, the power |
| A. | remains same |
| B. | reduced by a factor of 3 |
| C. | reduced by a factor of 2 |
| D. | increased by a factor of 2 |
| Answer» C. reduced by a factor of 2 | |