A small magnet has coercivity 3×10³ A/m. What current must pass through a solenoid of length 10 cm and 100 turns to demagnetise it?
Options

Question

A small magnet has coercivity 3×10³ A/m. What current must pass through a solenoid of length 10 cm and 100 turns to demagnetise it?

G1 Physics · Accepted Answer

For a solenoid, H=nI=NI/ℓ. To demagnetise, H equals the coercivity: 3×10³=(100/0.10)I, so I=3 A. Hence A.