Electrical and ...

An 820 Ω resistance with an accuracy of ± 10% carries a current of 10 mA. The current was measured by an analog meter of 25 mA range with an accuracy of ± 2% of full scale. The accuracy in the measurement of power dissipated in the resistor is

Two 50 V full scale PMMC DC voltmeter having figure of merits of 10 kΩ/V and 25 kΩ/V respectively are connected in series. The series combination can be used to measure a maximum DC voltage of _____ (in V)

Which of the instruments exists?

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 single-phase energy meter is tested for half an hour run at a supply voltage of 230 V and a load current of 10 A at a 0.8 lag power factor. The dial reading at the start was 57.35 and at the end of the test was 58.25. The error in meter registration in kWh is _______ (up to two decimal places)

Instrument transformers are

Which of the following instruments can be used to measure both AC and DC voltages?

A 300 V, 20 A dynamometer instrument is used as a wattmeter. Its current coil has 0.2 Ω resistance and pressure coil has 20 kΩ resistance with negligible inductance. What is the error in the instrument if it is used to measure the power in a circuit with supply voltage of 300 V, load current of 16 A at 0.4 pf. Assume that the pressure coil is connected across load side.

The following is a circuit representation of

The primary of a _______ should never be energised when its secondary is open circuited.

The primary of 200/1 A, 5 VA, 0.8 pf current transformer carries 100 A. The secondary current is 0.495 A. The ratio error of the CT is

A length of cable was tested for insulation resistance using loss of charge method. A capacitance formed by sheath of cable of 300 PF is found to have drop in voltage from 300 V to 100 V in 120 seconds. Calculate the insulation resistance of the cable in MΩ 

A current transformer has double turn primary and a 100 turn secondary winding. The secondary draws current of 6 A and magnetising ampere-turns is 60 A. What is actual transformation ratio?

Under operating conditions, the secondary of a current transformer is always short-circuited because of ________.

Power in a three-phase star-connected balanced inductive load is measured by two wattmeter method. The phase voltage and phase current are 200 V and 10 A respectively. The power factor of the load is 0.866. Which of the following is/are true regarding the wattmeter readings?

A dynamometer type wattmeter is rated at10 A and 400 V with a full-scale reading of 4000 W. the inductance of the voltage circuit is 6 mH and its resistance is 2000 Ω. If the operating frequency is 50 Hz and the voltage drop across the current coil of the wattmeter is negligible, the error in wattmeter at rated voltage and zero power factor will be ________W

A soft iron voltmeter for a minimum reading of 120 V has an inductance of 0.6 H and a total resistance of 2400 Ω. It is calibrated to read correctly at 60 Hz. The series resistance would be necessary to increase the range to 600 V is ______ (in kΩ)

In order to reduce skin effect in resistance standards when they are used on high frequency a.c.

The condition for a resistor to have the same value of resistance at medium frequencies as with d.c. is

A resistor R has an effective inductance of L and a distributed capacitance of C. its time constant at medium frequencies is

A 100 mv full-scale dual-slope \(3\frac 1 2\) digit DVM has a reference voltage of 75 mV and a first integration time of 75 ms. For an input of [60 + 20 sin (50 πt)] mV, which of the following is/are true?

A 100 Ω resistor has a time constant of 30 ns. What is the value of capacitor to be connected in parallel with the resistor to make its phase angle equal to zero?

For certain dynamometer ammeter, the mutual inductance M varies with deflection θ (expressed in degrees) as M = -5 cos (θ + 30°) mH. If the deflection torque produced by 60 mA current is 18 × 10^-6 N.m, the deflection of the instrument is _________(in degrees)

Each of the ratio arms of a laboratory type Wheatstone bridge has guaranteed accuracy of ±0.05%, while the standard arm has a guaranteed accuracy of ±0.1 %. The ratio arms are both set at 1 kΩ and and bridge is balanced with standard arm adjusted to 3154 Ω. The upper and the lower limits of the unknown resistance, based upon the guaranteed accuracies of the known bridge arms are respectively

A highly sensitive galvanometer can detect a current as low as 0.1 nA. This galvanometer is used in a Wheatstone bridge as a detector as shown in figure below. The resistance of galvanometer is negligible.

Each arm of the bridge has a resistance of 1 kΩ and the input voltage applied to bridge is 20 V. Neglecting the resistance of the galvanometer as compared with the internal resistance of bridge, the smallest change in the resistance which can be detected is