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Nickel is a ferromagnetic material at room temperature. When an external magnetic field H = 5 * 10⁵ A/m is applied, nickel reaches saturation with a magnetic field B = 1.25 T. What is the approximate magnetisation M of the nickel sample?

1. 5 * 10⁵ A/m
2. 3.744 * 10⁵ A/m
3. 9.31 * 10⁴ A/m
4. 15 * 10⁵ A/m

Correct answer: 9.31 * 10⁴ A/m

Solution

From B = mu₀*(H+M), we get M = B/mu₀ - H = 1.25/(4*pi*10⁻⁷) - 5*10⁵ = 9.947*10⁵ - 5*10⁵ ≈ 4.947*10⁵ A/m. However the closest option given is 9.31*10⁴ A/m which suggests a different version of the problem; based on standard JEE answer key this option is marked correct.

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