MCQOPTIONS
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MCQOPTIONS
This section includes 223 Mcqs, each offering curated multiple-choice questions to sharpen your Electronics knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
When does happen from the source to the load? |
| A. | When the source resistance is greater than the load resistance |
| B. | When the source resistance is less than the load resistance |
| C. | When there is negligible source resistance |
| D. | When the source resistance equals the load resistance |
| Answer» E. | |
| 2. |
A transformer is plugged into a 120 V rms source and has a primary current of 300 mA rms. The secondary is providing 18 V across a 10 load. What is the efficiency of the transformer? |
| A. | 88% |
| B. | 90% |
| C. | 92% |
| D. | 95% |
| Answer» C. 92% | |
| 3. |
What is the turns ratio of the transformer needed to match a 1 k source resistance to a 160 load? |
| A. | 2.5:1 |
| B. | 0.4:1 |
| C. | 6.25:1 |
| D. | 16:1 |
| Answer» C. 6.25:1 | |
| 4. |
A transformer turns ratio of ________ will be needed to match an output impedance of 5 k to an 8 speaker. |
| A. | 5:1 |
| B. | 8:1 |
| C. | 25:1 |
| D. | 625:1 |
| Answer» D. 625:1 | |
| 5. |
The changes in volume of transformer cooling oil due to variation of atmospheric temperature during day and night is taken care of by which part of transformer |
| A. | Conservator |
| B. | Breather |
| C. | Bushings |
| D. | Buchholz relay |
| Answer» B. Breather | |
| 6. |
The full-load copper loss of a trans¬former is 1600 W. At half-load, the copper loss willbe |
| A. | 6400 W |
| B. | 1600 W |
| C. | 800 W |
| D. | 400 W |
| Answer» E. | |
| 7. |
In a step-down transformer, there is a change of 15 A in the load current. This resultsin change of supply current of |
| A. | less than 15 A |
| B. | more than 15 A |
| C. | 15 A |
| D. | none of the above |
| Answer» B. more than 15 A | |
| 8. |
In an actual transformer the iron loss remains practically constant from noload tofullload because |
| A. | value of transformation ratio remains constant |
| B. | permeability of transformer core remains constant |
| C. | core flux remains practically constant |
| D. | primary voltage remains constant |
| Answer» D. primary voltage remains constant | |
| 9. |
The no load current in a transformer lags behind the applied voltage by an angle ofabout |
| A. | 180° |
| B. | 120" |
| C. | 90° |
| D. | 75° |
| Answer» E. | |
| 10. |
The efficiencies of transformers compared with that of electric motors of the samepower are |
| A. | about the same |
| B. | much smaller |
| C. | much higher |
| D. | somewhat smaller |
| Answer» D. somewhat smaller | |
| 11. |
The efficiency of two identical transformers under load conditions can bedetermined by |
| A. | short-circuit test |
| B. | back-to-back test |
| C. | open circuit test |
| D. | any of the above |
| Answer» C. open circuit test | |
| 12. |
Which of the following statements regarding an idel single-phase transformer having a turn ratio of 1 : 2 and drawing a current of 10 A from 200 V A.C. supply is incorrect ? |
| A. | Its secondary current is 5 A |
| B. | Its secondary voltage is 400 V |
| C. | Its rating is 2 kVA |
| D. | Its secondary current is 20 A |
| Answer» E. | |
| 13. |
The secondary winding of which of the following transformers is always kept closed ? |
| A. | Step-up transformer |
| B. | Step-down transformer |
| C. | Potential transformer |
| D. | Current transformer |
| Answer» E. | |
| 14. |
Which of the following acts as a protection against high voltage surges due to lightning and switching ? |
| A. | Horn gaps |
| B. | Thermal overload relays |
| C. | Breather |
| D. | Conservator |
| Answer» B. Thermal overload relays | |
| 15. |
The secondary of a current transformer is always short-circuited under operatingconditions because it |
| A. | avoids core saturation and high voltage induction |
| B. | is safe to human beings |
| C. | protects the primary circuit |
| D. | none of the above |
| Answer» B. is safe to human beings | |
| 16. |
If a transformer is continuously operated the maximum temperature rise will occurin |
| A. | core |
| B. | windings |
| C. | tank |
| D. | any of the above |
| Answer» C. tank | |
| 17. |
In a given transformer for given applied voltage, losses which remain constantirrespective of load changes are |
| A. | friction and windage losses |
| B. | copper losses |
| C. | hysteresis and eddy current losses |
| D. | none of the above |
| Answer» D. none of the above | |
| 18. |
Which of the following protection is normally not provided on small distributiontransformers ? |
| A. | Overfluxing protection |
| B. | Buchholz relay |
| C. | Overcurrent protection |
| D. | All of the above |
| Answer» C. Overcurrent protection | |
| 19. |
In a given transformer for a given applied voltage, losses which remain constantirrespective of load changes are |
| A. | hysteresis and eddy current losses |
| B. | friction and windage losses |
| C. | copper losses |
| D. | none of the above |
| Answer» B. friction and windage losses | |
| 20. |
An ideal transformer has infinite values of primary and secondary inductances. Thestatement is |
| A. | true |
| B. | false |
| C. | none |
| D. | none |
| Answer» C. none | |
| 21. |
Ifthe percentage impedances of the two transformers working in parallel are different, then |
| A. | transformers will be overheated |
| B. | power factors of both the trans-formers will be same |
| C. | parallel operation will be not possible |
| D. | parallel operation will still be possible, but the power factors at which the two transformers operate will be different from the power factor of the common load |
| Answer» E. | |
| 22. |
What will happen if the transformers working in parallel are not connected with regard to polarity ? |
| A. | The power factor of the two trans-formers will be different from the power factor of common load |
| B. | Incorrect polarity will result in dead short circuit |
| C. | The transformers will not share load in proportion to their kVA ratings |
| D. | none of the above |
| Answer» C. The transformers will not share load in proportion to their kVA ratings | |
| 23. |
Auto-transformer makes effective saving on copper and copper losses, when itstransformation ratio is |
| A. | approximately equal to one |
| B. | less than one |
| C. | great than one |
| D. | none of the above |
| Answer» B. less than one | |
| 24. |
Losses which occur in rotating electric machines and do not occur in trans formersare |
| A. | friction and windage losses |
| B. | magnetic losses |
| C. | hysteresis and eddy current losses |
| D. | copper losses |
| Answer» B. magnetic losses | |
| 25. |
Current transformers for meters and relays usually has |
| A. | 1 : 2 ratio |
| B. | 5 : 1 ratio |
| C. | 5 - A secondary's |
| D. | 15 - A secondary's |
| Answer» D. 15 - A secondary's | |
| 26. |
An industrial analyser is NOT suitable for measuring which of the following? |
| A. | Power |
| B. | Resistance |
| C. | Current |
| D. | Power factor |
| Answer» C. Current | |
| 27. |
A current carrying conductor is wrapped eight times around the jaw of a clamp-on meter that reads 50 A. What will be the actual value of the conductor current? |
| A. | 400 A |
| B. | 6.25 A |
| C. | 50 A |
| D. | 12.5 A |
| Answer» C. 50 A | |
| 28. |
In the current transformer, the number of primary turns is always: |
| A. | less than the number of secondary turns |
| B. | zero |
| C. | greater than the number of secondary turns |
| D. | equals the number of secondary turns |
| Answer» B. zero | |
| 29. |
Power of a 1-phase 3.3 kV load drawing a current of 50 A is required to be measured by means of a wattmeter having potential terminals marked as 110 V and current terminals as 5 A. What is the transformation ratio of the CT? |
| A. | 20 A |
| B. | 0.2 A |
| C. | 10 A |
| D. | 0.1 A |
| Answer» D. 0.1 A | |
| 30. |
If the secondary winding of a current transformer is opened when the primary winding is carrying current, then the following event occurs: |
| A. | Transformer will burn immediately |
| B. | High induced EMF is produced in the secondary winding |
| C. | Flux density in the core gets weakened |
| D. | High current is produced in the secondary winding |
| Answer» C. Flux density in the core gets weakened | |
| 31. |
In the case of a potential transformer (PT), the phase angle error is |
| A. | positive when the secondary winding voltage reversed leads the primary winding voltage |
| B. | negative when the secondary winding voltage reversed leads the primary winding voltage |
| C. | always positive |
| D. | always negative |
| Answer» B. negative when the secondary winding voltage reversed leads the primary winding voltage | |
| 32. |
Burden of current transformer is usually expressed in |
| A. | Amperes |
| B. | Volts |
| C. | Volt amperes |
| D. | Kilowatt |
| Answer» D. Kilowatt | |
| 33. |
A current transformer (CT) of turns ratio 1 : 248 is rated as 1000 / 4 A, 20 VA. The core loss and magnetizing components of the primary current are 4 A and 8 A under rated conditions. The ratio error for the rated burden and the rated secondary current at 0.8 power factor lagging is |
| A. | 0 |
| B. | -0.64 |
| C. | -0.66 |
| D. | 0.8 |
| Answer» E. | |
| 34. |
In using instrument transformers, care should be taken not to open circuit the |
| A. | primary of a voltage transformer when the secondary is connected to the rated load |
| B. | secondary of a voltage transformer when the primary is energized with the rated voltage |
| C. | primary of a current transformer when the secondary is connected to the rated load |
| D. | secondary of a current transformer when the primary is carrying the rated current |
| Answer» E. | |
| 35. |
In current transformers, turn compensation is provided to reduce the |
| A. | power losses |
| B. | ratio error |
| C. | phase angle error |
| D. | ratio and phase angle errors |
| Answer» C. phase angle error | |
| 36. |
A 50Hz, bar primary CT has a secondary with 500 turns. The secondary supplies 5 A current into a purely resistance burden of 1 Ω. The magnetizing ampere – turns is 200. The phase angle between the primary and secondary current is |
| A. | 4.6° |
| B. | 85.4° |
| C. | 94.6° |
| D. | 175.4° |
| Answer» B. 85.4° | |
| 37. |
A transformer is an electrical device that transfer electrical energy from one electric circuit to another, without changing: |
| A. | Capacitance |
| B. | Current |
| C. | Frequency |
| D. | Voltage |
| Answer» D. Voltage | |
| 38. |
An instrument transformer is used to extend the range of- |
| A. | Induction instrument |
| B. | Electrostatic instrument |
| C. | Moving coil instrument |
| D. | PMMC instrument/PMMC |
| Answer» B. Electrostatic instrument | |
| 39. |
A current transformer has a phase error of +3°. The phase angle between the primary and secondary currents is |
| A. | 3° |
| B. | 177° |
| C. | 180° |
| D. | 183° |
| Answer» C. 180° | |
| 40. |
Consider the following statements regarding error occurring in current transformer:1. It is due to the magnetic leakage in secondary winding.2. It is due to power consumption in the metering circuit3. It is due to the exciting mmf required by the primary winding to produce flux4. It is due to the non-linear relation between flux density in the core and magnetizing forceWhich of the above statements are correct? |
| A. | 1, 2, 3 and 4 |
| B. | 1, 2 and 4 only |
| C. | 2, 3 and 4 only |
| D. | 1, 2 and 3 only |
| Answer» E. | |
| 41. |
In which of the following transformers is the secondary current of the same order as that of the magnetizing current? |
| A. | Potential transformers |
| B. | Current transformers |
| C. | Power transformers |
| D. | Distribution transformers |
| Answer» C. Power transformers | |
| 42. |
A current transformer (CT) of turns ratio 1 : 248 is rated as 1000 / 4 A, 20 VA. The core loss and magnetizing components of the primary current are 4 A and 8 A under rated conditions, the phase angle error for the rated burden and the rated secondary current at 0.8 power factor lagging is |
| A. | \(\frac 1 {496} rad\) |
| B. | \(\frac 1 {248} rad\) |
| C. | \(\frac 1 {124} rad\) |
| D. | \(\frac 1 {62} rad\) |
| Answer» C. \(\frac 1 {124} rad\) | |
| 43. |
Manganese ferrite is 1: 1 mixture of |
| A. | Manganese nitride and iron oxide |
| B. | Manganese oxide and iron oxide |
| C. | Manganese nitride and iron supplied |
| D. | Manganese oxide and iron sulphate |
| Answer» C. Manganese nitride and iron supplied | |
| 44. |
A current transformer has a phase error of +5 degree. The phase angle between the primary and secondary current is: |
| A. | 5 degree |
| B. | 95 degree |
| C. | 175 degree |
| D. | 85 degree |
| Answer» D. 85 degree | |
| 45. |
In which of the following transformers, the secondary winding is always kept closed? |
| A. | Current transformer |
| B. | Potential transformer |
| C. | Power transformer |
| D. | Distribution transformer |
| Answer» B. Potential transformer | |
| 46. |
A Buchholz relay can be installed on |
| A. | auto-transformers |
| B. | air-cooled transformers |
| C. | welding transformers |
| D. | oil cooled transformers |
| Answer» E. | |
| 47. |
An ideal transformer will have maximum efficiency at a load such that |
| A. | copper loss = iron loss |
| B. | copper loss < iron loss |
| C. | copper loss > iron loss |
| D. | none of the above |
| Answer» B. copper loss < iron loss | |
| 48. |
If the percentage impedances of the two transformers working in parallel are different, then |
| A. | transformers will be overheated |
| B. | power factors of both the transformers will be same |
| C. | parallel operation will be not possible |
| D. | parallel operation will still be possible, but the power factors at which the two transformers operate will be different from the power factor of the common load |
| Answer» E. | |
| 49. |
A good voltage regulation of a transformer means |
| A. | output voltage fluctuation from no load to full load is least |
| B. | output voltage fluctuation with power factor is least |
| C. | difference between primary and secondary voltage is least |
| D. | difference between primary and secondary voltage is maximum |
| Answer» B. output voltage fluctuation with power factor is least | |
| 50. |
The purpose of providing an iron core in a transformer is to |
| A. | provide support to windings |
| B. | reduce hysteresis loss |
| C. | decrease the reluctance of the magnetic path |
| D. | reduce eddy current losses |
| Answer» D. reduce eddy current losses | |