A rectangular coil of 120 turns and an area of 10 × 10 - 4 m 2 is suspended in a radial magnetic field of 45 × 19 - 4 T . If a current of 2 mA through the coil gives it a deflection of 36 ° . Find the effective torsion constant for the spring system holding the coil.

Given the number of turns n = 120 . Area of the coil A = 10 × 10 - 4 m 2 . The radial magnetic field B = 45 × 10 - 4 T . The current in the coil I = 2 mA . Deflection θ = 36 ° ' The current in the galvanometer is given by I = k nBA θ or k = nBAI θ where k = torsion constant of the galvanometer spring, Substituting the values, we have, k = 120 × 45 × 10 - 4 × 10 × 10 - 4 × 2 × 10 - 3 36 = 3 . 0 × 10 - 9 Nm / degree Hence the torsion constant of the galvanometer is 3 × 10 - 9 Nm / degree

EASY

Earn 100

Given below are two statements:

Statement I: If the number of turns in the coil of a moving coil galvanometer is doubled then the current sensitivity becomes double.

Statement II: Increasing current sensitivity of a moving coil galvanometer by only increasing the number of turns in the coil will also increase its voltage sensitivity in the same ratio

In the light of the above statements, choose the correct answer from the options given below:

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Important Questions on Magnetic Effect of Electric Current

EASY

Science>Physics>Magnetic Effect of Electric Current>Galvanometer

The resistance of the required shunt in order to pass

10 %

of the main current in a galvanometer of

99 Ω

resistance should be

HARD

Science>Physics>Magnetic Effect of Electric Current>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

Science>Physics>Magnetic Effect of Electric Current>Galvanometer

Describe the construction of suspended coil galvanometer, draw labelled diagram of it. Prove that current flowing in the coil of galvanometer is directly proportional to the deflection generated in the coil.

EASY

Science>Physics>Magnetic Effect of Electric Current>Galvanometer

The number of turns of the coil of a moving coil galvanometer is increased in order to increase current sensitivity by

50 %

. The percentage change in voltage sensitivity of the galvanometer will be :

MEDIUM

Science>Physics>Magnetic Effect of Electric Current>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

MEDIUM

Science>Physics>Magnetic Effect of Electric Current>Galvanometer

For a moving coil galvanometer, the deflection in the coil is

0.05 rad

when a current of

10 mA

is passed through it. If the torsional constant of suspension wire is

4.0 \times 10^{- 5} N m {rad}^{- 1}

, the magnetic field is

0.01 T

and the number of turns in the coil is

200

, the area of each turn (in

{cm}^{2}

) is :

HARD

Science>Physics>Magnetic Effect of Electric Current>Galvanometer

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

HARD

Science>Physics>Magnetic Effect of Electric Current>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.

MEDIUM

Science>Physics>Magnetic Effect of Electric Current>Galvanometer

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

HARD

Science>Physics>Magnetic Effect of Electric Current>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?

EASY

Science>Physics>Magnetic Effect of Electric Current>Galvanometer

The current sensitivity of moving coil galvanometer is increased by

25 %

. This increase is achieved only changing in the number of turns of coils and area of cross section of the wire while keeping the resistance of galvanometer coil constant. The percentage change in the voltage sensitivity will be:

EASY

Science>Physics>Magnetic Effect of Electric Current>Galvanometer

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

MEDIUM

Science>Physics>Magnetic Effect of Electric Current>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]:

Question Image

HARD

Science>Physics>Magnetic Effect of Electric Current>Galvanometer

A rectangular coil of

120 turns

and an area of

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

is suspended in a radial magnetic field of

45 \times 19^{- 4} T

. If a current of

2 mA

through the coil gives it a deflection of

36 °

. Find the effective torsion constant for the spring system holding the coil.

MEDIUM

Science>Physics>Magnetic Effect of Electric Current>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:

EASY

Science>Physics>Magnetic Effect of Electric Current>Galvanometer

This question has

Statement I

and

Statement II

. Of the four choices given after the Statements, choose the one that best describes the two Statements.

Statement - I :

Higher the range, greater is the resistance of ammeter.

Statement - II :

To increase the range of ammeter, additional shunt needs to be used across it.

EASY

Science>Physics>Magnetic Effect of Electric Current>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:

HARD

Science>Physics>Magnetic Effect of Electric Current>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?

MEDIUM

Science>Physics>Magnetic Effect of Electric Current>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

EASY

Science>Physics>Magnetic Effect of Electric Current>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?

Important Questions on Magnetic Effect of Electric Current

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