Name: Principle and Working of a Cyclotron
Uploaded: 2019-07-19
Duration: 6 min 12 s
Description: Can a magnetic field be used to accelerate a charged particle? Are you curious to know which device will do this job? Let's find out through this video.

Question

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.

Accepted Answer

Advantages and disadvantages of a moving coil galvanometer are:-

Advantages:-

1) High sensitivity

2) Not easily affected by stray magnetic fields

3) Torque to weight ratio is high

4) High accuracy and reliability

Disadvantages:-

1) It can be only used to measure direct current.

2) Develops errors due to factors like aging of the instrument, magnets and damage of spring due to mechanical stress.

Given, Number of turns, $N = 10$

Length of coil, $L = 12 cm$

Breadth of coil, $b = 8 cm$

Current in the coil, $I = 125 μA$

Magnetic field in the region, $B = 10^{- 2} T$ ,

Twist Constant, $k = 12 \times 10^{- 9} Nm / degree$

Now torque on coil due to magnetic field

$τ = F \times b$

$= B I L \times b$

$= B I A$

For n coils $τ = n I A B$

Now let the coil deflect through $θ$

Then opposite torque due to phosphor bronze fibre

$τ = k θ$ kθ

Now, at equilibrium

$k θ = n I A B$

$θ = k n I A B$

$θ = 12 \times 10^{- 9} \times 10 \times 125 \times 10^{- 6} \times 12 \times 10^{- 2} \times 8 \times 10^{- 2} \times 10^{- 2} = 10 °$

Important Questions on Magnetic Effect of Electric Current

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