SATHEE: Magnetics 5 Question 2

Magnetics 5 Question 2

2. 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 $1^{\circ}$ for a current of $1 m A$ . The value of $B$ (in Tesla) is approximately (2019 Main, 9 April II)

(a) $10^{- 3}$

(b) $10^{- 4}$

(d) $10^{- 2}$

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Answer:

Correct Answer: 2. (a)

Solution:

In a moving coil galvanometer in equilibrium, torque on coil due to current is balanced by torque of torsion band.

As, torque on coil,

where, $B =$ magnetic field strength,

$I =$ current,

$N$ =number of turns of coil

Since, plane of the coil is parallel to the field.

$∴ α = 90^{\circ} \Rightarrow τ = N I B A$

Torque of torsion band, $T = k θ$

where, $k =$ torsion constant of torsion band

and $θ =$ deflection of coil in radians or angle of twist of restoring torque.

$∴ B I N A = k θ or B = \frac{k θ}{I N A}$

Here,

$\begin{aligned} k & = 10^{- 6} N - m / r a d, \\ I & = 1 \times 10^{- 3} A, \\ N & = 175, \\ A & = 1 c m^{2} = 1 \times 10^{- 4} m^{2} \\ θ & = 1^{\circ} = \frac{π}{180} r a d \end{aligned}$

Substituting values in Eq. (i), we get

$\begin{aligned} B & = \frac{10^{- 6} \times 22}{1 \times 10^{- 3} \times 175 \times 7 \times 180 \times 10^{- 4}} \\ = 0.998 \times 10^{- 3} ≃ 10^{- 3} T \end{aligned}$

Magnetics 5 Question 2

2. A moving coil galvanometer has a coil with 175 turns and area $1 c m^{2}$ . It uses a torsion band of torsion constant

Answer:

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Magnetics 5 Question 2

2. A moving coil galvanometer has a coil with 175 turns and area 1cm2. It uses a torsion band of torsion constant

Answer:

Engineering Preparation

Medical Preparation

NCERT Books & Solutions

Important Resources

Other Resources

Syllabus

Test Platform

Sample Mock Test

Mentorship

NCERT Exercise Video Solution

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2. A moving coil galvanometer has a coil with 175 turns and area $1 c m^{2}$ . It uses a torsion band of torsion constant