The principal axis is also called ______ of the lens.

Options

A. optical axis
B. x-axis
C. y-axis
D. axis

Answer

**Step-by-Step Solution:**

1. **Understanding the Principal Axis**: The principal axis of a lens is an important concept in optics. It is defined as the line that passes through the optical center of the lens and is perpendicular to the surface of the lens.

2. **Identifying Alternate Names**: The principal axis can be referred to by different names. One commonly accepted alternative name is the "optical axis."

3. **Conclusion**: Therefore, the principal axis is also called the "optical axis" of the lens.

**Final Answer**: The principal axis is also called the **optical axis** of the lens.

---