Question

Magnetic susceptibility ($\chi$) of paramagnetic materials follows:

• A. Curie's Law ($\chi \propto 1/\text{T}$)
• B. Ohm's law
• C. Hooke's law
• D. Wiedemann–Franz law

Hint:

If the material is ferromagnetic, above its Curie Temperature ($T_c$), it transitions into a paramagnet and follows the Curie-Weiss Law:
$\chi = \frac{C}{T - \theta}$

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks which physical law governs the temperature dependence of the magnetic susceptibility of paramagnetic materials.

Step 2: Key Formula or Approach:
Curie's Law states that the magnetic susceptibility of a paramagnetic material is inversely proportional to its absolute temperature:
\[ \chi = \frac{C}{T} \]
where:
$C$ is the material-specific Curie constant.
$T$ is the absolute temperature in Kelvin.

Step 3: Detailed Explanation:

• In a paramagnetic material, the alignment of atomic magnetic dipoles with an external field is opposed by random thermal motion.

• As the temperature ($T$) of the material increases, the thermal kinetic energy of the atoms increases. This causes greater randomization of the dipole directions.

• Consequently, the net magnetization decreases for a given applied field, which directly reduces the susceptibility ($\chi$).

• This inverse relationship is expressed as $\chi \propto 1/T$, which is known as Curie's Law.

• Other options like Ohm's law (electricity), Hooke's law (elasticity), and Wiedemann–Franz law (thermal/electrical conductivity ratio) are completely unrelated to magnetic susceptibility.

Step 4: Final Answer:
The susceptibility follows Curie's Law ($\chi \propto 1/T$).