A coil has 2000 turns and an area of 70cm². The magnetic field perpendicular to the plane of the coil is 0.3 Wb/m² and takes 0.1 sec to rotate through 180°. The value of the induced e.m.f. will be:
Correct answer: B. 84V
- A. 8.4V
- B. 84V
- C. 42V
- D. 4.2V
Explanation
The induced emf is given by Faraday's Law, ε = -N (ΔΦ/Δt). The change in flux (ΔΦ) for a 180° rotation is from BA to -BA, so ΔΦ = 2BA. Plugging in the values gives ε = -2000 × (2 × 0.3 T × 0.007 m²) / 0.1 s = -84 V. The magnitude is 84V.
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Magnetic flux density and magnetic flux describe the strength of a magnetic field and the field passing through a surface. A charged particle moving through a magnetic field experiences a force perpendicular to its velocity and may follow circular or helical motion, depending on the angle between velocity and field.
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