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What is the working principle of moving coil galvanometer?

Important Questions on Magnetic Fields due to Electric Current

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Physics>Electricity and Magnetism>Magnetic Fields due to Electric Current>Moving Coil Galvanometer

The deflection in a moving coil galvanometer is reduced to half when it is shunted with

X Ω

coil. The relation between

X

and resistance of galvanometer

G

HARD

Physics>Electricity and Magnetism>Magnetic Fields due to Electric Current>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 ?

EASY

Physics>Electricity and Magnetism>Magnetic Fields due to Electric Current>Moving Coil Galvanometer

To increase the current sensitivity of a moving coil galvanometer by

50 %,

its resistance is increased, so that new resistance becomes twice its initial resistance, by what factor does its voltage sensitivity change?

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Physics>Electricity and Magnetism>Magnetic Fields due to Electric Current>Moving Coil Galvanometer

The current sensitivity of a moving coil galvanometer depends on,

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Physics>Electricity and Magnetism>Magnetic Fields due to Electric Current>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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MEDIUM

Physics>Electricity and Magnetism>Magnetic Fields due to Electric Current>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 Fields due to Electric Current>Moving Coil Galvanometer

A moving coil galvanometer has resistance

50 Ω

and it indicates full deflection at

4 m A

current. A voltmeter is made using this galvanometer and a

5 k Ω

resistance. The maximum voltage, that can be measured using this voltmeter, will be close to:

EASY

Physics>Electricity and Magnetism>Magnetic Fields due to Electric Current>Moving Coil Galvanometer

Define current sensitivity of a galvanometer. Write its expression.

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Physics>Electricity and Magnetism>Magnetic Fields due to Electric Current>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 Fields due to Electric Current>Moving Coil Galvanometer

A moving coil galvanometer has a coil with

175

turns and area

1 c m^{2} .

It uses a torsion band of torsion constant

10^{- 6} N m / r a d

The coil is placed in a magnetic field B parallel to its plane. The coil deflects by

1^{o}

for a current of

1 m A

The value of B (in tesla) is approximately:

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Physics>Electricity and Magnetism>Magnetic Fields due to Electric Current>Moving Coil Galvanometer

The reason a moving coil galvanometer cannot be used with an alternating current is that

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Physics>Electricity and Magnetism>Magnetic Fields due to Electric Current>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

EASY

Physics>Electricity and Magnetism>Magnetic Fields due to Electric Current>Moving Coil Galvanometer

A galvanometer of resistance

50 Ω

is connected to battery of

3 V

along with a resistance of

2950 Ω

in series. A full scale deflection of 30 divisions is obtained in the galvanometer. In order to reduce this deflection to

20

divisions, the resistance in series should be

HARD

Physics>Electricity and Magnetism>Magnetic Fields due to Electric Current>Moving Coil Galvanometer

State the advantages and disadvantages of a moving coil galvanometer.A moving coil galvanometer (M.C.G.) has

10

10 turns each of length

12 cm

and breadth

8 cm

. The coil of M.C.G. carries a current of

125 μA

and is kept perpendicular to the uniform magnetic field of induction

10^{- 2} T

. The twist constant of phosphor bronze fibre is

12 \times 10^{- 9} Nm / degree

. Calculate the deflection produced.

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Physics>Electricity and Magnetism>Magnetic Fields due to Electric Current>Moving Coil Galvanometer

The current sensitivity of moving coil galvanometer of resistance

100 Ω

1 div / mA .

Its voltage sensitivity is

HARD

Physics>Electricity and Magnetism>Magnetic Fields due to Electric Current>Moving Coil Galvanometer

What is moving coil galvanometer? Draw labelled diagram of suspended coil galvanometer and prove that the deflection of a coil is directly proportional to the current flowing through it.

EASY

Physics>Electricity and Magnetism>Magnetic Fields due to Electric Current>Moving Coil Galvanometer

Phosphor-bronze wire is used for suspension in a moving coil galvanometer, because it has:

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Physics>Electricity and Magnetism>Magnetic Fields due to Electric Current>Moving Coil Galvanometer

The resistance of a galvanometer is

50 o h m

and the maximum current which can be passed through it is

0.002 A .

What resistance must be connected to it in order to convert it into an ammeter of range

0 - 0.5 A ?

MEDIUM

Physics>Electricity and Magnetism>Magnetic Fields due to Electric Current>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:

HARD

Physics>Electricity and Magnetism>Magnetic Fields due to Electric Current>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.

What is the working principle of moving coil galvanometer?

Important Questions on Magnetic Fields due to Electric Current

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