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The figure of merit of a galvanometer is defined as

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Important Questions on Magnetic Effect of Current

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Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

The sensitivity of tangent galvanometer is increased, if

HARD

Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

Consider two identical galvanometers and two identical resistors with resistance

R

. If the internal resistance of the galvanometers

R_{c} < \frac{R}{2},

which of the following statement(s) about any one of the galvanometers is(are) true ?

MEDIUM

Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

A galvanometer, whose resistance is

50 ohm

, has

25

divisions in it. When a current of

4 \times 10^{- 4}

A passes through it, its needle (pointer) deflects by one division. To use this galvanometer as a voltmeter of range

2.5 V

it should be connected to a resistance of:

HARD

Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

In a circuit for finding the resistance of a galvanometer by half deflection method, a

6 V

battery and a high resistance of

11 kΩ

are used. The figure of merit of the galvanometer is

60 μA {division}^{- 1}

. In the absence of shunt resistance, the galvanometer produces a deflection of

θ = 9

divisions when current flows in the circuit. The value of the shunt resistance that can cause the deflection of

\frac{θ}{2}

, is closest to:

MEDIUM

Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

For full scale deflection of total

50

divisions,

50 mV

voltage is required in galvanometer. The resistance of galvanometer if its current sensitivity is

2 div / mA

will be:

EASY

Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

A circuit contains an ammeter, a battery of 30 v and a resistance 40.8 ohm all connected in series. If the ammeter has coil of resistance 480 ohm and a shunt of 20 ohm, the reading in the ammeter will be:

MEDIUM

Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

The galvanometer deflection, when key $K_{1}$ is closed but $K_{2}$ is open, equals $θ_{0}$ (see figure). On closing $K_{2}$ also and adjusting $R_{2}$ to $5 Ω,$ the deflection in galvanometer becomes $\frac{θ_{0}}{5} .$ The resistance of the galvanometer is, then, given by [Neglect the internal resistance of battery]:

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Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

A galvanometer having a coil resistance of

100 Ω

gives a full scale deflection, when a current of

1 mA

is passed through it. The value of the resistance, which can convert this galvanometer into ammeter giving a full scale deflection for a current of

10 A

, is:

MEDIUM

Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

Current sensitivity of a moving coil galvanometer is

5 d i v / m A

and its voltage sensitivity (angular deflection per unit voltage applied) is

20 d i v / V

. The resistance of the galvanometer is

MEDIUM

Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

The current sensitivity of a moving coil galvanometer depends on,

EASY

Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

A galvanometer with its coil resistance

25 Ω

requires a current of

1 mA

for its full deflection. In order to construct an ammeter to read up to a current of

2 A

the approximate value of the shunt resistance should be:

EASY

Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

Write the definition of figure of merit of Galvanometer.

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Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

When a current of

5 mA

is passed through a galvanometer having a coil of resistance

15 Ω

, it shows full-scale deflection. The value of the resistance to be put in series with the galvanometer to convert it into a voltmeter of range

0 - 10 V

is:

HARD

Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

A moving coil galvanometer has 50 turns and each turn has an area

2 \times 10^{- 4} m^{2}

. The magnetic field produced by the magnet inside the galvanometer is

0.02 T

. The torsional constant of the suspension wire is

10^{- 4} N m {rad}^{- 1}

. When a current flows through the galvanometer, a full scale deflection occurs if the coil rotates by

0.2 rad

. The resistance of the coil of the galvanometer is

50 Ω

. This galvanometer is to be converted into an ammeter capable of measuring current in the range

0 - 1.0 A

. For this purpose, a shunt resistance is to be added in parallel to the galvanometer. The value of this shunt resistance, in ohms, is

α

. Write the value of

[α]

, where

[]

is the greatest integer function.

EASY

Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

Sensitivity of moving coil galvanometer is

s

. If a shunt of

{(\frac{1}{8})}^{t h}

of the resistance of galvanometer is connected to moving coil galvanometer, its sensitivity becomes

MEDIUM

Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

A galvanometer has a 50 division scale. Battery has no internal resistance. It is found that there is deflection of 40 divisions when $R.B. = 2400 Ω .$ Deflection becomes 20 divisions when resistance taken from resistance box is 4900 Ω. Then we can conclude :

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Note: This question is awarded as the bonus. Now the question is corrected.

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Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

To know the resistance

G

of a galvanometer by half deflection method, a battery of emf

V_{E}

and resistance

R

is used to deflect the galvanometer by angle

θ

. If a shunt of resistance

S

is needed to get half deflection the

G

R

and

S

are related by the equation:

MEDIUM

Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

A millivoltmeter of

25 mV

range is to be converted into an ammeter of

25 A

range. The value (in ohm) of necessary shunt will be

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Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

In a moving coil galvanometer, when the number of turns of the coil is doubled,

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Physics>Electricity and Magnetism>Magnetic Effect of Current>Sensitivity and Accuracy of Moving Coil Galvanometer

The number of turns in a coil of Galvanometer is tripled, then

The figure of merit of a galvanometer is defined as

Important Questions on Magnetic Effect of Current

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