Which of the following statement is true ?

Options

A. Piezo - electricity is due to net dipole moment
B. Ferro - electricity is due to alignment of dipoles in same direction
C. Piezo - electricity is due to heating polar crystals
D. All of the above

Answer

To determine which of the statements regarding piezoelectricity, ferroelectricity, and pyroelectricity is true, let's analyze each concept step by step.

### Step 1: Understanding Piezoelectricity
- **Definition**: Piezoelectricity is the electric charge that accumulates in certain materials in response to applied mechanical stress.
- **Key Fact**: It is related to the net dipole moment of the material. When mechanical stress is applied, the dipoles within the material become polarized, leading to an electric charge.

**Hint**: Remember that piezoelectricity involves mechanical stress causing a charge due to dipole alignment.

### Step 2: Understanding Ferroelectricity
- **Definition**: Ferroelectricity refers to materials that exhibit spontaneous electric polarization that can be reversed by the application of an external electric field.
- **Key Fact**: Ferroelectricity occurs when the dipoles in the material are aligned in the same direction. This alignment leads to a net dipole moment that can be switched.

**Hint**: Think of ferroelectricity as a state where all dipoles are aligned, creating a strong overall dipole moment.

### Step 3: Understanding Pyroelectricity
- **Definition**: Pyroelectricity is the ability of certain materials to generate an electric charge in response to a change in temperature.
- **Key Fact**: Pyroelectricity arises from the heating of polar crystals, where the dipole moment is not zero. When these crystals are heated, the change in temperature causes a change in polarization, leading to an electric charge.

**Hint**: Pyroelectricity is all about temperature changes affecting the dipole moment in polar materials.

### Step 4: Evaluating the Statements
- **Statement 1**: Piezoelectricity is due to the net dipole moment. **(True)**
- **Statement 2**: Ferroelectricity is due to the alignment of dipoles in the same direction. **(True)**
- **Statement 3**: Pyroelectricity is due to heating of polar crystals. **(True)**

### Conclusion
Since all three statements are true, the correct answer is:
- **Option 4: All of the above.**

**Final Answer**: Option 4 is the correct option and the required answer for this question.

---