Sample 1Medium
A horizontal circular loop of wire of radius 10 cm carries a current of 5 A that flows anticlockwise as seen from above. Take μ₀ = 4π × 10⁻⁷ T m/A. What is the magnetic field at the centre of the loop?
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The answer is C.
B = μ₀I/2R = (4π × 10⁻⁷ × 5)/(2 × 0.1) = π × 10⁻⁵ T. By the right-hand rule, an anticlockwise current seen from above gives a field pointing upward at the centre.
- A.
The magnitude is right, but an anticlockwise current gives an upward field.
- B.
2π × 10⁻⁵ T omits the factor 2 in μ₀I/2R.
- D.
π × 10⁻⁷ T misses the conversion of 10 cm to 0.1 m.
NCERT: Class 12 Physics, Chapter 4