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JEE Main 2020 (4 Sep, Shift 2) · Magnetic Materials & Curie Law

Magnetic Materials & Curie Law question from JEE Main 2020 (4 Sep, Shift 2)

Q26JEE Main 2020 · 4 SEP · SHIFT 2Medium

Magnetic Materials & Curie Law

A paramagnetic sample shows a net magnetisation of 6 A/m when it is placed in an external magnetic field of 0.4 T at a temperature of 4 K. When the sample is placed in an external magnetic field of 0.3 T at a temperature of 24 K, then the magnetisation will be:

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Answer: (c)

  1. Curie's law: M=χHM = \chi H with χ∝1T\chi \propto \dfrac{1}{T}, so M∝BTM \propto \dfrac{B}{T}.
  2. M2M1=B2B1⋅T1T2=0.30.4×424=18\dfrac{M_2}{M_1} = \dfrac{B_2}{B_1} \cdot \dfrac{T_1}{T_2} = \dfrac{0.3}{0.4} \times \dfrac{4}{24} = \dfrac{1}{8}
  3. M2=68=0.75 A/mM_2 = \dfrac{6}{8} = 0.75\text{ A/m}
  4. So the answer is (c) 0.75 A/m.
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