Which is true

Options

A. Piezoelectricity is due to net - dipole movement
B. Some electric current is produced on heating polar crystals, this is pyro electricity
C. Ferroelectricity is due to allignment of dipole in the same direction
D. All of the above

Answer

To solve the question, we need to analyze each statement regarding piezoelectricity, pyroelectricity, and ferroelectricity to determine their validity.

### Step-by-Step Solution:

1. **Analyzing Statement 1: Piezoelectricity is due to the net dipole moment.**
- **Explanation**: Piezoelectricity refers to the generation of electric charge in certain materials when mechanical stress is applied. This phenomenon occurs in polar crystals where the displacement of ions leads to a net dipole moment. Therefore, this statement is **true**.

2. **Analyzing Statement 2: Some electric current is produced on heating polar crystals (pyroelectricity).**
- **Explanation**: Pyroelectricity is the ability of certain materials to generate an electric current when they are heated or cooled. When polar crystals are subjected to temperature changes, they produce a small electric current. Thus, this statement is also **true**.

3. **Analyzing Statement 3: Ferroelectricity is due to the alignment of the dipole in the same direction.**
- **Explanation**: Ferroelectric materials have a spontaneous polarization that can be reversed by the application of an external electric field. In these materials, the dipoles align in the same direction, similar to ferromagnetism. Therefore, this statement is **true**.

4. **Analyzing Statement 4: All of the above.**
- **Explanation**: Since all the previous statements (1, 2, and 3) have been determined to be true, this statement is also **true**.

### Conclusion:
Since all statements are correct, the answer to the question "Which is true?" is **Option 4: All of the above**.

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