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Define sensitivity of a moving coil galvanometer. Derive an expression for current sensitivity of a moving coil galvanometer.

Important Questions on Magnetism and Magnetic Effects of Electric Current

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Physics>Electricity Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and 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 Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and 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 Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and 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 Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and Moving Coil Galvanometer

The current sensitivity of a moving coil galvanometer depends on,

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Physics>Electricity Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and 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 Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and 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

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Physics>Electricity Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and 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:

HARD

Physics>Electricity Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and Moving Coil Galvanometer

What is the basic principle of moving coil galvanometer?. Derive an expression for the current flowing through the galvanometer in terms of the steady angular deflection of its coil. Define voltage sensitivity of the galvanometer. What is a convenient way to increase its sensitivity?

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Physics>Electricity Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and 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:

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Physics>Electricity Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and 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:

EASY

Physics>Electricity Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and Moving Coil Galvanometer

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

EASY

Physics>Electricity Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and 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

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Physics>Electricity Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and Moving Coil Galvanometer

A coil in the shape of an equilateral triangle of side

10 cm

lies in a vertical plane between the pole pieces of permanent magnet producing a horizontal magnetic field

20 mT

. The torque acting on the coil when a current of

0.2 A

is passed through it and its plane becomes parallel to the magnetic field will be

\sqrt{x} \times 10^{- 5} Nm

. The value of

x

HARD

Physics>Electricity Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and 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 Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and Moving Coil Galvanometer

Derive the expression for the torque acting on the rectangular current carrying coil of a galvanometer. Why is the magnetic field made radial?

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Physics>Electricity Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and Moving Coil Galvanometer

Describe with principle, the construction and working of a moving coil galvanometer.

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Physics>Electricity Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and Moving Coil Galvanometer

Describe the principle and working of a moving coil galvanometer and hence show that the deflection of the coil is directly proportional to the current flowing through it. What is the effect of the radial magnetic field in a moving coil galvanometer?

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Physics>Electricity Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and 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 ?

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Physics>Electricity Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and 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 Magnetism>Magnetism and Magnetic Effects of Electric Current>Torque on the Loop Placed in a Magnetic Field and 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.

Define sensitivity of a moving coil galvanometer. Derive an expression for current sensitivity of a moving coil galvanometer.

Important Questions on Magnetism and Magnetic Effects of Electric Current

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