Equivalent Voltmeter and Ammeter

Q. A moving coil ammeter has a uniform scale with 50 divisions and gives a full scale reading of 10 A. The instrument can read up to (1/5)th of a scale division with a fair degree of certainity. The resolution of the instrument (in mA) is _____.

1. 0.4
2. 4
3. 0.04
4. 40

Q. A (0-10) mA PMMC ammeter reads 4 mA in a circuit. Its bottom control spring snaps suddenly. The meter will now read nearly

1. 10 mA
2. 8 mA
3. 2 mA
4. zero

Q. The inductance of a certain moving-iron ammeter is expressed as:
$L=10+3\theta -\left({\theta }^2/4\right)\mu H$, where $\theta$ is the deflection in radians from the zero position. The control spring torque in $25\times {10}^{-6}Nm/radian.$ The deflection of the pointer in radian when the meter carries a current of 5 A, is

1. 2.4
2. 2.0
3. 1.2
4. 1.0

Q. In the Permanent Magnet Moving Coil (PMMC) instruments, damping is provided by

1. The coil spring attached to the moving coil
2. The aluminium frame to the moving coil
3. Damping vane in the air tight chamber
4. Eddy current disk

Q. The coil of a moving coil voltmeter is 40 mm long and 30 mm wide and has 100 turns on it. The control spring exerts a torque of $240\times {10}^{-6}N-m$ when the deflection is 100 divisions on full scale. If the flux density of the magnetic field in the airgap is $1.0Wb/m^2$, the resistance that must be put in series with the coil to give one volt per division is ________$\Omega$. (Assume resistance of the voltmeter coil is negligible)

1. $500k\Omega$
2. $50k\Omega$
3. $5k\Omega$
4. $1k\Omega$

Q. Two 100 V full scale PMMC type dc voltmeter having figure of merits (FOM) of $10k\Omega /V$ and $20k\Omega /V$ are connected in series. The series combination can be used to measure a maximum DC voltage of ____V.

1. 150

Q. The inductance of a moving iron ammeter is given by the expression $L=(10+5\theta -2{\theta }^2)\mu H$, where $\theta$ is the angular deflection in radians from zero position. Angular deflection (in degrees) for a current of 10 A if the deflection for a current of 5 A is ${45}^o$ is

1. ${54.7}^o$
2. ${56.7}^o$
3. ${62.41}^o$
4. ${73.5}^o$

Q. The inductance of a moving iron instrument is given by $L=(10+5\theta -{\theta }^2)$ $\mu H$, where $\theta$ is the deflection in degree from zero position. The spring constant is $3\times {10}^{-6}Nm/degree$ then the deflection for a currrent of 5 A.

1. 2.23 rad
2. 2.23 degree
3. 127.76 degree
4. 8.03 rad

Q. A 1 mA meter d'Arsonaval movement with an internal resistance of $100\Omega$ is to be converted into a 0 - 100 mA ammeter. The value of shunt resistance required is ______ $\Omega$.

1. 0.101
2. 1.01
3. 100
4. 1.1

Q. A rectifier type PMMC voltmeter has a sensitivity of $20k\Omega /V.$ A reading of 4.5 V is obtained when measuring a voltage source with an internal resistance on it's 5 V scale. When the scale is changed to 10 V full scale, a reading of 6 V is obtained. The value of the voltage and it's internal resistance R are

1. $10Vand100k\Omega$
2. $9Vand100k\Omega$
3. $10Vand200k\Omega$
4. $9Vand200k\Omega$

Q. A moving iron voltmeter calibrated for 50 Hz supply and having an inductance of the coil as 0.80 H draws 0.1 A when connected to 500 V AC. What will be its reading when connected to 300 V DC supply?

1. 300.4 V
2. 150 V
3. 175.8 V
4. 325.6 V

Q. The current coil of a dynamometer type wattmeter is connected to a 24 V dc source in series with a 6 $\Omega$ resistor. The potential circuit is connected through an ideal half wave rectifier in series with a 50 Hz source of 100 V. The inductance of pressure circuit and current coil resistance are negligible. The reading of wattmeter is

1. 80.5 W
2. 180 W
3. 362 W
4. 148.7 W

Q. The inductance of a moving iron instrument is given by $L=(18+5\theta -4{\theta }^2)\mu H$, (where is the deflection in radian from zero position). If the spring constant is ${10}^{-5}$ Nm/rad, the deflection for 5 A current will be

1. 1.69 radian
2. 0.568 radian
3. 32.54 degree
4. 96.82 degree

Q. A periodic voltage waveform observed on an oscilloscope across a load is shown. A permanent magnet moving coil (PMMC) meter connected across the same load reads

1. 4 V
2. 5 V
3. 8 V
4. 10 V

Q. The input impedance of the permanent magnet moving coil (PMMC) voltmeter is infinite. Assuming that the diode shown in the figure below is ideal, the reading of the voltmeter in Volts is

1. 4.46
2. 3.15
3. 2.23
4. 0

Q. For the network shown in the figure, the voltage across terminal AB is measured by a voltmeter. The sensitivity of voltmeter is $2k\Omega /volt$. Which of the following statement is true?

1. $\text{Voltmeter has 27.27\% error}$
2. $\text{Resistance of voltmeter =}100k\Omega$
3. $\text{Voltage across CD = 33.33 V}$
4. $\text{Equivalent resistance across CD = 36.36 k}\Omega$

Q. The PMMC ammeter A in the adjoining figure has a range of 0 to 3 mA. When switch $S_1$ is opened, the pointer of the ammeter swings to the 1 mA mark, returns and settles at 0.9 mA. The meter is

1. critically damped and has a coil resistance of $100\Omega$
2. Critically damped and has a coil resistance of $200\Omega$
3. under damped and has a coil resistance of $100\Omega$
4. under damped and has a coil resistance of $200\Omega$

Q. The copper coil of a 150 volts moving iron voltmeter has a resistance of 400 $\Omega at{15}^o$ and an inductance of 0.75 H. The current for full-scale deflection is 0.05 A. The temperature coefficient of resistance for copper and eureka at ${15}^{o}C$ are 0.004 and 0.00001 respectively. The percentage increase of resistance of the instrument per degree rise in temperature is __________%.

1. 0.5
2. 0.05
3. 5
4. 0.005

Q. A manganin swamp resistance is connected in series with a moving coil ammeter consisting of a milli-ammeter and a suitable shunt in order to

1. minimize the effect of temperature variation.
2. reduce the size of the meter
3. obtain large deflecting torque.
4. minimize the effect of stray magnetic fields.

Q. A periodic voltage waveform observed in an oscilloscope across load is shown below. A moving iron (MI) meter connected across the same load reads_______volts(Answer upto 2 decimal pleaces).

1. 8.41
2. 0.841
3. 10
4. 84.1

Q. Two same voltage rating PMMC type DC voltmeters having figure of merit of $10k\Omega /V$ and $25k\Omega /V$ respectively are connected in series. This series combination of voltmeters can measure maximum of 280 V. The voltage rating of voltmeters will be ______V.

1. 200

Q. Two 100 V full scale PMMC type DC voltmeters having sensitivity of $2k\Omega /Vand4k\Omega /V$ are connected in series. The series combination can be used to measure a dc voltage of _________V.

1. 100 V
2. 200 V
3. 150 V
4. 160 V

Q. A periodic voltaage waveform observed on oscilloscope of a load is shown in figure.

Which of these given statements(s) is/are correct?

1. when PMMC voltmeter is connected across load, then it will reads 4 V.
2. when MI voltmeter is connected across load then it will also reads 4 V.
3. PMMC instrument always reads rms value.
4. Moving iron instrument can read only rms value.

Q. An input voltage represented by waveform as shown below is applied to a moving iron instrument. The reading of the instrument will be _______ V.

1. 1.0
2. 0.132
3. 1.32
4. 0.32

Q. Reading obtained when a voltage of $e=200\sin \omega t+40\sin (3\omega t+30{}^{\circ })+30\cos (5\omega t+21.5{}^{\circ })$ is applied is to an electrodynamometer voltmeter is ________ V.

1. 140
2. 145.77
3. 154.77
4. 150