A 250 -Turn rectangular coil of length 2.1 cm and width 1.25 cm carries a current of 85μ A and subjected to a magnetic field of strength 0.85 T. Work done for rotating the coil by 180 ° against the torque is:

Correct answer: A. 9.1μ J W = MB(cos θ _ 1 - cos θ _ 2 ) When it is rotated by angle 180 ^ o then θ _ 1 = 0 ° and θ _ 2 = 180 ° W = 2MB W = 2(NIA)B = 2 × 250 × 85 × 10 ^ - 6 [1.25 × 2.1 × 10 ^ - 4 ] × 85 × 10 ^ - 2 = 9.1μ J

NEET 2017

Exam: NEET
Year: 2017
Subject: Physics
Chapter: Magnetic Effects of Current

NEET 2017 · Physics · Magnetic Effects of Current

A 250 -Turn rectangular coil of length 2.1 cm and width 1.25 cm...

250

-Turn rectangular coil of length

2.1 cm

and width

1.25 cm

carries a current of

85\mu A

and subjected to a magnetic field of strength

0.85 T.

Work done for rotating the coil by

180 °

against the torque is:

Options

A $9.1\mu J$
B $4.55\mu J$
C $2.3\mu J$
D $1.15\mu J$

Correct answer

A. $9.1\mu J$

Step-by-step solution

W = MB\left(cos {\theta}_{1} - cos {\theta}_{2}\right)

When it is rotated by angle

{180}^{o}

then

{\theta}_{1} = 0 °

and

{\theta}_{2} = 180 °

W = 2MB

W = 2\left(NIA\right)B

= 2 \times 250 \times 85 \times {10}^{- 6}\left[1.25 \times 2.1 \times {10}^{- 4}\right] \times 85 \times {10}^{- 2}

= 9.1\mu J

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