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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.
| 51. |
The accuracy of measurement by ohmmeter is very good. |
| Answer» It is very low. | |
| 52. |
As per BIS, the number of accuracy classes of instrument is |
| Answer» 8 losses. | |
| 53. |
In most of instruments, the controlling torque is provided by |
| Answer» Eddy current damping is very common. | |
| 54. |
A 0-200 V voltmeter has a sensitivity of 1 kΩ per volt. The resistance of voltmeter is |
| Answer» 200 x 1 kΩ. | |
| 55. |
DC ampere hour meter is an indicating instrument. |
| Answer» It is an integrating instrument. | |
| 56. |
The loss of charge method can be used to measure |
| Answer» It is used for measuring very high resistance. | |
| 57. |
Current density has the dimensions |
| Answer» Current density = current/area = IL-2. | |
| 58. |
The resistance of a dc galvanometer is 20 Ω. A current of 10 mA causes full scale deflection. To convert it into 0-300 V voltmeter, we have to use a series resistance of |
| Answer» . | |
| 59. |
Hay's bridge is suitable for inductances having low L/R ratio. |
| Answer» It is suitable for high ratio inductances. | |
| 60. |
Moving iron instrument can be used for ac only. |
| Answer» Moving iron instruments can be used for both dc and ac. | |
| 61. |
In electronic voltmeters the measuring device is a |
| Answer» The a.c. voltage is rectified and measured by PMMC instrument. | |
| 62. |
An ammeter has a resistance of 50 ohms and a shunt of 0.01 Ω. The deflection is θ. If the shunt resistance is increased to 0.02 Ω, the deflection will be. |
| Answer» Since shunt resistance is doubled, current through ammeter is doubled (current division for resistances in parallel). Therefore reading is 2 θ. | |
| 63. |
The ac bridge in figure is balanced. Z = 100∠30°, Z = 150∠0°, Z = 250∠ - 40° Then Z = |
| Answer» . | |
| 64. |
The most commonly used moving iron instruments are |
| Answer» Repulsion type have better accuracy. | |
| 65. |
A moving iron instrument can be used for |
| Answer» Its deflecting torque ∝ I2. So, it can be used for both d.c. and a.c. | |
| 66. |
Two voltmeters are each 0-300 V range. Their internal resistances are 10 kΩ and 20 kΩ They are connected is series and a voltage of 400 V is applied. Their readings respectively will be |
| Answer» The readings will be proportional to their internal resistance, . | |
| 67. |
A 300 V voltmeter has an accuracy of ± 2% of full scale deflection. When the reading is 222 V, the actual voltage |
| Answer» Error = ± 6 V. Therefore, the actual value would be between 222 ± 6 V. | |
| 68. |
The sensitivity of a voltmeter using 0-5 mA meter movement is |
| Answer» . | |
| 69. |
A moving coil meter has 10 Ω resistance and requires 40 mA for full scale deflection. The shunt resistance required to convert it into 0-2 A ammeter is |
| Answer» . | |
| 70. |
The torque in induction wattmeters due to |
| Answer» Eddy currents are induced in the disc. | |
| 71. |
Two resistances are : R = 36 Ω ± 1.89 Ω and R = 75 Ω ± 3.75 Ω. The sum R + R along with limiting error is |
| Answer» 36 + 75 = 111, 1.8 + 3.75 = 5.55. Therefore, R1 + R2 = 111 ± 5.55 ohm. | |
| 72. |
A generated voltage is equally dependent on three resistances R, R, R and its value is V = (RR)/R. If tolerance of each resistor is 0.1%, the maximum error in voltage is |
| Answer» The tolerances are additive. | |
| 73. |
The current through a resistance is shown in figure. The computed value of power is |
| Answer» % error in current is 2% and % error in resistance is 0.2%. Since P = I2R, % error in power = 2 x 2% + 0.2% = 4.2%. | |
| 74. |
The resistance in the circuit of the moving coil of a dynamometer wattmeter should be |
| Answer» Moving coil is voltage coil and must have high resistance. | |
| 75. |
What would be the reading of voltmeter as shown in below figure. The voltmeter has a 0-1 V scale and is a 20000 Ω/V meter |
| Answer» Effective resistance of circuit . | |
| 76. |
A temperature sensistive transducer is subjected to sudden temperature change. It takes 10 seconds for transducer to reach equilibrium condition (five times time constant). The time taken to reach half of temperature difference will be |
| Answer» The initial change is fast. | |
| 77. |
Figure shows a Wheatstone bridge with RTD to one arm. If resistance of RTD = 1020 Ω, the voltage V is |
| Answer» | |
| 78. |
A capacitance transducer can be used to measure |
| Answer» In all these, change of capacitance occurs. | |
| 79. |
The dynamometer principle can be used for |
| Answer» Dynamometer principle can be used for ammeter, voltmeter and wattmeter. However it is generally used for wattmeters only. | |
| 80. |
The scale of hot wire ammeter is |
| Answer» Since deflecting torque ∞ I2, scale is non-linear. | |
| 81. |
A moving coil meter has a shunt of 0.02 Ω resistance. If coil resistance is 1000 Ω and a potential difference of 500 mV is required across it to cause full scale deflection, the current through shunt is |
| Answer» . | |
| 82. |
A resistance is measured by voltmeter-ammeter method. The voltmeter is 0-250V, ± 1% accuracy and ammeter is 0-5 A, ± 1 % accuracy. The readings of voltmeter and ammeter are 100 V and 2 A respectively. The error in the measured resistance can be |
| Answer» Error in voltmeter can be ± 2.5 V which for 100 V reading is ± 2.5 % . Error in ammeter can be ± 0.05 A which for 2 A reading is ± 2.5 %. Hence total error can be ± 5%. | |
| 83. |
It is required to study transients during switching process. Which CRO should be preferred? |
| Answer» We can store the trace. | |
| 84. |
If the secondary winding of CT is opened when primary coil is carrying current |
| Answer» Since the primary of CT always remains excited, a high voltage is induced in secondary if the secondary is opened. | |
| 85. |
The percentage limiting error in an instrument reading 8.3 V and having guaranteed accuracy of 1% of the full scale reading and range of 0-150 V is |
| Answer» Error = 1% of 150 = 1.5 V, . | |
| 86. |
A meter has a resistance of 1 Ω and full scale deflection current of 1 mA. To convert into an ammeter of 1 A range, the shunt resistance should be |
| Answer» Resistance of shunt . | |
| 87. |
Two wattmeter method is suitable only for balanced loads. |
| Answer» It is suitable for both balanced and unbalanced loads. | |
| 88. |
A rectifier voltmeter using bridge rectifier and PMMC meter is calibrated to read rms value of sine wave. A triangular wave is applied to it and it reads 6.82 V. The rms value of triangular wave is |
| Answer» Peak value of triangular wave is twice average value = 2 x 6.144 = 12.288 V rms value of triangular wave is peak value divided by 3 . Therefore, reading . | |
| 89. |
A radiation thermometer is suitable for temperatures |
| Answer» It is suitable for only very high temperatures. | |
| 90. |
The effect of lead resistance is important in measurement of |
| Answer» Lead resistance is important when measuring low resistance. Resistance of shunt and ammeter is low. | |
| 91. |
A high resistance was measured by loss of charge method. The voltmeter resistance was 10 ohms. The calculation gave the value of unknown resistance as 0.8 x 10 ohms. The true value of resistance is |
| Answer» Let unknown resistance be R. Evidently R is more than 0.8 x 109 ohm. | |
| 92. |
A resistance wire strain gauge has gauge factor 2. If stress is 100 mega newton/m and Young's modulus is 200 giga newton/ m, the percentage change in gauge resistance due to stress is |
| Answer» . | |
| 93. |
The current passing through a resistance of 100 ± 0.2% Ω is 2 ± 0.5% A. The limiting error in computation of power will be |
| Answer» Limiting error = 2 x 0.5 + 0.2 = ± 1.2% (we have to take 2 x 0.5 because power ∝ I2). | |
| 94. |
If the secondary burden of a CT 15 VA and secondary current is 5 A, the load impedance of CT is |
| Answer» . | |
| 95. |
A 0-150 voltmeter has a guaranteed accuracy of 1% of full scale reading. If actual reading is 83 V, the percentage error is |
| Answer» . | |
| 96. |
In a CRO, the frequency of output of time base generator |
| Answer» Time base signal frequency is adjustable so that voltages of different frequencies can be measured. | |
| 97. |
If A = 131 ± 4 and B = 106 ± 4, the percentage range of doubt in A - B is |
| Answer» (A - B) = 25 ± 8. Therefore, % range of doubt . | |
| 98. |
Two resistance R and R are connected in series R = 528 ± 5 Ω and R = 325 ± 3Ω. The total resistance will be |
| Answer» Both errors can be positive or negative simultaneously. Hence 853 ± 8 Ω. | |
| 99. |
The function of shunt in an ammeter is to |
| Answer» It bypasses a major portion of circuit current so that only the rated current of meter can flow through the meter. | |
| 100. |
It is necessary to measure the amplitudes of two signals and also the phase difference between them. This can be done by using a |
| Answer» A waveform meter is suitable to study amplitudes, phase angles etc. of different waveforms. | |