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Concepts Of Physics MCQ Edition [Volume 2]
Exam
Concepts Of Physics MCQ Edition [Volume 2]
Subject
Physics
Chapter
Permanent Magnets

Concepts Of Physics MCQ Edition [Volume 2] · Physics · Permanent Magnets

A moving-coil galvanometer contains a 50 -turn coil with dimensions...

A moving-coil galvanometer contains a 5050-turn coil with dimensions 2 cm×2 cm2 \text{ cm} \times 2 \text{ cm}. It is suspended between magnetic poles that produce a magnetic field of 0.5 T0.5 \text{ T}. Determine the torque exerted on the coil by the magnetic field when a current of 20 mA20 \text{ mA} flows through it.

Options

  1. A2×10−5 N m2 \times 10^{-5} \text{ N m}
  2. B4×10−4 N m4 \times 10^{-4} \text{ N m}
  3. C2×10−4 N m2 \times 10^{-4} \text{ N m}
  4. D1×10−4 N m1 \times 10^{-4} \text{ N m}

Correct answer

C. 2×10−4 N m2 \times 10^{-4} \text{ N m}

Step-by-step solution

Given:

N=50N = 50

A=2 cm×2 cm=4×10−4 m2A = 2 \text{ cm} \times 2 \text{ cm} = 4 \times 10^{-4} \text{ m}^2

B=0.5 TB = 0.5 \text{ T}

I=20 mA=20×10−3 AI = 20 \text{ mA} = 20 \times 10^{-3} \text{ A}

The torque on the coil in a moving-coil galvanometer with a radial magnetic field is given by:

τ=NIAB\tau = NIAB

Substituting the given values:

τ=50×(20×10−3)×(4×10−4)×0.5\tau = 50 \times (20 \times 10^{-3}) \times (4 \times 10^{-4}) \times 0.5

τ=1000×10−3×2×10−4\tau = 1000 \times 10^{-3} \times 2 \times 10^{-4}

τ=1×2×10−4=2×10−4 N m\tau = 1 \times 2 \times 10^{-4} = 2 \times 10^{-4} \text{ N m}
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