Concepts Of Physics MCQ Edition [Volume 2]PhysicsPermanent Magnets
A long bar magnet possesses a pole strength of 10 Am . Determine the magnetic field at a point situated on the magnet's axis, at a distance of 5 cm from its north pole.
Options
- A8 10⁻⁴ T
- B4 10⁻⁴ T
- C2 10⁻⁵ T
- D4 10⁻⁸ T
Correct answer
B. 4 10⁻⁴ T
Step-by-step solution
Since the bar magnet is long, the magnetic field at a point near one of its poles is effectively due to that pole alone. The contribution from the other pole is negligible. The magnetic field B at a distance r from a magnetic pole of strength m is given by: B = ₀ 4 m r^2 Given m = 10 Am and r = 5 cm = 0.05 m . Substituting the values: B = 10⁻⁷ 10 (0.05)^2 B = 10⁻⁷ 10 25 10⁻⁴ B = 10⁻⁷ 4000 B = 4 10⁻⁴ T