Electrical and electronics measurements miscellaneous Difficult Questions and Answers | Page - 10

Electrical and electronics measurements miscellaneous

A compensat ed wattmeter has its reading corrected for error due to the

1. frequency
1. friction
1. power consumed in current coil
1. power consumed in potential coil

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A compensated wattmeter has its reading corrected for error due to power consumed in potential coil.

Correct Option: D

A compensated wattmeter has its reading corrected for error due to power consumed in potential coil.

The effective reactance of an inductive coil

1. increases because of stray capacitance as the frequency increases
1. decreases because of stray capacitances as the frequency increases
1. remain the same irrespective of the increase in frequency even if stray series capacitances are present
1. none of these

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NA

Correct Option: B

NA

A closed coil spring has a stiffness of 20 × 10^-6 N/m. If diameter of the wire is doubled, its outer diameter is made two times and its number of turns are made two times, the stiffness of then new spring will be

1. 20 × 10^-6 N/m
1. 80 × 10^-6 N/m
1. 10 × 10^-6 N/m
1. 160 × 10^-6 N/m

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NA

Correct Option: A

NA

A simple d.c. potentiometer is to be standardised by keeping the sidewire setting at 1. 0813 V. If by mistake, the setting is at 1.0138 V and the standardisation is made to obtain a source voltage of 1.0318 V, then the reading of the potentiometer will be

1. 1.0138 V
1. 1.0183 V
1. (1.0138)²/ 1.0183 V
1. (1.0138)² V

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The setting of the potentiometer is at 1.0138 instead of 1.0813. Therefore, working current in the slide wise is more than what it would have been if the setting was at 1.0813,
i.e. correct value for applied voltage of 1.0813V,
I = 1.0813, I_c = 1.0138
It the setting is at 1.01138 and the applied voltage is also 1.0138 and the applied voltage is also 1.0138, the standardisation is then correct. (Statement of the problem appears ambiguous).

Correct Option: C

The setting of the potentiometer is at 1.0138 instead of 1.0813. Therefore, working current in the slide wise is more than what it would have been if the setting was at 1.0813,
i.e. correct value for applied voltage of 1.0813V,
I = 1.0813, I_c = 1.0138
It the setting is at 1.01138 and the applied voltage is also 1.0138 and the applied voltage is also 1.0138, the standardisation is then correct. (Statement of the problem appears ambiguous).

The power in a resistor R is estimated by measuring the voltage and current using the voltmeterammeter method. Two different arrangements can be used as shown in circuits I and II. Less erroneous results are obtained by adopting

1. circuit I for low values of R
1. circuit II for values of R
1. circuit I for values of R
1. circuit II for low and high values of R

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For low resistance measurements, if circuit II is used, the ammeter resistance which may be comparable with the low resistance being measured gets added to the unknown and thereby causing larger error.

Correct Option: A

For low resistance measurements, if circuit II is used, the ammeter resistance which may be comparable with the low resistance being measured gets added to the unknown and thereby causing larger error.