Choose the correct alternative (a), (b), (c) or (d) for each of the questions given below :
Curie temperature is the temperature above which :

Options

A. a ferromagnetic substance behaves like a paramagnetic substance.
B. a paramagnetic substance behaves like a diamagnetic substance.
C. a ferromagnetic substance behaves like a diamagnetic substance.
D. a paramagnetic substance behaves like a ferromagnetic substance.

Answer

To solve the question regarding the Curie temperature, we will analyze the options step by step.

**Step 1: Understanding Curie Temperature**
- The Curie temperature (Tc) is a critical temperature for ferromagnetic materials. Below this temperature, the material exhibits ferromagnetism, meaning it can maintain a permanent magnetic moment. Above this temperature, the thermal energy disrupts the alignment of magnetic moments, leading to a loss of ferromagnetism.

**Step 2: Analyzing the Options**
- **Option A:** A ferromagnetic substance behaves like a paramagnetic substance.
- This statement is true. Above the Curie temperature, ferromagnetic materials lose their ordered magnetic moment and behave like paramagnets, which are only magnetized in the presence of an external magnetic field.

- **Option B:** A paramagnetic substance behaves like a diamagnetic substance.
- This statement is incorrect. Paramagnetic substances are attracted to magnetic fields, while diamagnetic substances are repelled by them. They do not transform into one another based on temperature alone.

- **Option C:** A ferromagnetic substance behaves like a diamagnetic substance.
- This statement is also incorrect. While ferromagnetic materials lose their ferromagnetic properties above the Curie temperature, they do not behave like diamagnetic substances.

- **Option D:** A paramagnetic substance behaves like a ferromagnetic substance.
- This statement is incorrect. Paramagnetic substances do not exhibit ferromagnetism; they require specific conditions to show magnetic properties.

**Step 3: Conclusion**
- Based on the analysis, the correct answer is **Option A:** A ferromagnetic substance behaves like a paramagnetic substance above the Curie temperature.

**Final Answer:**
The correct alternative is (a) A ferromagnetic substance behaves like a paramagnetic substance.

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