InterviewSolution
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InterviewSolution
This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
A 1 mA meter is to be converted to 1 A ammeter. The meter resistance is 100 Ω. The value of shunt resistance is |
| Answer» . | |
| 2. |
The use of thermocouple meters for ac measurement leads to a scale which is |
| Answer» Thermocouple meter is based on heating effect which varies as I2. | |
| 3. |
The current in a circuit is measured using a 150 : 1 CT If the ammeter reads 0.6 A, the circuit current is |
| Answer» 150 x 0.6 = 90 A. | |
| 4. |
A volt ratio box should have low resistance. |
| Answer» It should have high resistance. | |
| 5. |
A Hall effect transducer has K = - 1 x 10. If B = 1 Wb/m, I = 3 A and bismuth slab is 2 mm wide, the Hall voltage is |
| Answer» . | |
| 6. |
Two ammeters A and B both 0-10 A have internal resistance of 1 Ω and 0.5 Ω respectively. They are connected in parallel. If total current is 15 A, then |
| Answer» Currents divide in inverse proportion of resistances. . | |
| 7. |
A meter having 0-1000 μA range and 1000 Ω resistance is required to be changed to 0-100 mA meter. The value of shunt resistance is about |
| Answer» . | |
| 8. |
An induction wattmeter can be used for |
| Answer» Induction principle is valid for ac only. Induction Instruments are calibrated for 50 Hz ac. | |
| 9. |
In the balanced bridge shown in figure. should be |
| Answer» Since two primary of CT always remains, a high voltage is induced in secondary if the secondary is opened. | |
| 10. |
If the current in a capacitor leads the voltage by 80°, the loss angle of capacitor is |
| Answer» Loss angle δ = 90 - 80 = 10°. | |
| 11. |
Which of these has poor overload capacity? |
| Answer» The wire is very delicate and has little over load capacity. | |
| 12. |
In 3 phase power measurement by two wattmeter method, both wattmeters had equal reading. The power factor of load is |
| Answer» Readings of two wattmeters are same when σ = 0 or p.f. = 1. | |
| 13. |
Which instrument is based on induction principle? |
| Answer» Energy meter is also based on induction principle. | |
| 14. |
Magnetic field intensity has the dimensions |
| Answer» Magnetic field intensity = MMF/length = IL-1. | |
| 15. |
Two voltmeters 0-250 V each having resistances of 5 kΩ and 10 kΩ respectively and are connected in series. To ensure that neither of them goes beyond scale the total voltage which can be applied should be less than |
| Answer» or V = 375 V. | |
| 16. |
A 24 mm long conductor has a resistance of 128 Ω. The change in resistance is 13.3 Ω and change in length is 1.6 mm under tension. The gauge factor is |
| Answer» . | |
| 17. |
Measuring of unknown voltage with a dc potentiometer loses its advantage of open circuit measurement when |
| Answer» When volt ratio box is used to reduce range, the advantage of open-circuit measurement is lost. | |
| 18. |
In figure, the position of voltmeter and ammeter are exchanged. It may result in damage to |
| Answer» Very high current will flow through ammeter because ammeter resistance is very low. | |
| 19. |
The volt ratio box is basically a |
| Answer» DC potentiometer can measure voltages upto about 1.5 V. Volt ratio box is used to reduce the unknown voltage so that it can be measured by dc potentiometer. | |
| 20. |
A sinusoidal ac voltage of amplitude 100 V is applied to a rectifying device which offers 10 Ω resistance in forward direction and infinite resistance in backward direction. A moving coil ammeter is also connected in the circuit. The reading of ammeter will be |
| Answer» Moving coil instrument indicates average value . | |
| 21. |
A variable reluctance tachometer has 180 teeth on rotor. The speed of shaft on which it is mounted in 1200 rpm. The frequency of output pulses is |
| Answer» . | |
| 22. |
In the wheatstone bridge in figure, each resistance is increased by 0.05%. The value of v will be |
| Answer» Output of first op-amp is -2V, -V2. Therefore, . | |
| 23. |
In a digital measuring device the input electrical signal is in the frequency range of dc to ac (50) Hz. It must be sampled at a rate of |
| Answer» Sampling frequency must be twice the input frequency. | |
| 24. |
A meter has a square law scale. For 2 A current the deflection in 90°. For a deflection of 45°, the current is |
| Answer» | |
| 25. |
PCM employing 4 bit code is used to send data having frequency range from 0 to 2 kHz. The minimum required bandwidth of carrier channel is |
| Answer» Bandwidth required is twice the required frequency range. | |
| 26. |
A sinusoidal ac voltage of amplitude 100 V is applied to a rectifying device which offers 10 Ω resistance in forward direction and infinite resistance in reverse direction. The reading on hot wire ammeter will be |
| Answer» Hot wire ammeter indicates rms value . | |
| 27. |
When a capacitor is connected to the terminals of an ohmmeter, the pointer indicated a low resistance initially and finally come to infinity position. This shows that capacitor is |
| Answer» Capacitor behaves as short circut initially and open circuit finally when fed by dc supply. | |
| 28. |
The power input and output in a device are 3650 W and 3385 W with each reading in doubt by ± 10 W. The percentage uncertainty in losses is |
| Answer» Losses = 3650 - 3385 = 265 W uncertainty = ± 20 W. . | |
| 29. |
A meter coil has a resistance of 100 Ω and a full scale deflection current of 10 mA. To convert it into a voltmeter of 0-200 V range, the series resistance should be |
| Answer» . | |
| 30. |
Which of these has a magnetic brake? |
| Answer» Braking torque, in an energy meter, is provided by a magnet. | |
| 31. |
Two numbers are 131 ± 5 and 629 ± 3. The sum of the numbers with range of doubt is |
| Answer» The numbers can be 131 + 5, 131 - 5, 629 - 3. Therefore, the sum can be 760 ± 8. | |
| 32. |
If eddy current damping is to be used, the disc of instrument should be |
| Answer» Disc must be conducting otherwise eddy currents can not flow. It must be non-magnet, i.e., so that it does not affect the measurement. | |
| 33. |
The scale of moving iron instrument is linear. |
| Answer» Since reading is proportional to I2, the scale is non-linear. | |
| 34. |
With a variable reluctance tachometer having 60 rotor teeth the count reads 3600 counts per minute. The speed in RPM is |
| Answer» If speed is 60, the counter will count 60 x 60 = 3600 counts/per minute. | |
| 35. |
When measuring phase angle between two waves using a CRO, the time base generator is connected to |
| Answer» Time base signal is not connected. The two waves are fed to X and Y plates respectively. | |
| 36. |
It is required that a strain gauge has gauge factor of 100. The proper strain gauge is |
| Answer» Only semiconductor strain gauge can have a gauge factor of 100. For all other strain gauges, gauge factor is about 2 only. | |
| 37. |
LVDT is a |
| Answer» It is used to measure displacement. | |
| 38. |
A 0-200 V voltmeter has an accuracy of 0.75% of full scale reading. If voltage measured is 100 V, the error is |
| Answer» . | |
| 39. |
In Schering bridge, the potential of detector above earth potential is about |
| Answer» 136 | |
| 40. |
The dimensions of EMF are |
| Answer» EMF = workdone/charge. | |
| 41. |
Electrostatic voltmeter is suitable only for low voltages. |
| Answer» It is suitable for high voltage. | |
| 42. |
An accelerometer has a seismic mass of 0.05 kg and spring constant of 3 x 10 N/m. If maximum displacement of mass is ± 1 mm, the maximum acceleration which can be measured is |
| Answer» 0.05 x a = 3 x 103 x 10-3 or a = 60 m/s2. | |
| 43. |
If an inductance L is connected in one arm of bridge and resistance R, R, R in other three arms |
| Answer» To balance the bridge both magnitudes and phase angles of voltages have to be balanced. | |
| 44. |
A moving iron voltmeter reads 250 V when connected to 250 V dc. If connected to 250 V 50 Hz, the voltmeter reading is likely to be |
| Answer» The inductance of coil will allow slightly less ac current. Hence reading slightly less. | |
| 45. |
A single element strain gauge bridge has two fixed resistances R and R of 120 Ω each and a variable resistance which gives full deflection at 120 Ω for zero strain and 120.6 Ω for straine . If gauge factor is 2, strain is |
| Answer» . | |
| 46. |
In an induction wattmeter, the shading bands are made of non conducting material. |
| Answer» The shading bands are of conducting material. | |
| 47. |
Kelvin's double bridge is used to measure low resistances because |
| Answer» Effect of lead and contact resistances is very important in measurement of low resistances. | |
| 48. |
The scale of hot wire instrument is linear. |
| Answer» Since reading is proportional to I2, the scale is non-linear. | |
| 49. |
The D'Arsonval- movement can be converted into audio frequency ac ammeter by adding a |
| Answer» Rectifier converts ac to dc which is measured by D'Arsonval meter. | |
| 50. |
The resistance of a 125 Ω strain gauge changes by 1 ohm for 4000 micro strain. The gauge factor is |
| Answer» . | |