The line joining the pole and the centre of curvature of a mirror is called the

Options

A. aperture
B. principal section
C. principal axis
D. pole

Answer

To solve the question, we need to identify the correct term for the line that connects the pole of a mirror to its center of curvature. Let's break down the solution step by step.

### Step-by-Step Solution:

1. **Understand the Components of a Mirror:**
- A spherical mirror has several important components, including the pole (P), the center of curvature (C), and the principal axis.

2. **Identify the Pole and Center of Curvature:**
- The pole (P) is the midpoint of the mirror's surface.
- The center of curvature (C) is the center of the sphere from which the mirror is a part.

3. **Define the Line Joining the Pole and Center of Curvature:**
- The line that connects the pole (P) to the center of curvature (C) is a straight line that runs through the mirror.

4. **Recognize the Term Used for This Line:**
- This specific line is referred to as the "Principal Axis" of the mirror.

5. **Eliminate Other Options:**
- The term "Principal Section" does not refer to this line.
- The term "Pole" refers to the point on the mirror's surface, not the line.
- The term "Aperture" refers to the opening or the surface area of the mirror.

6. **Conclusion:**
- Therefore, the correct answer to the question is that the line joining the pole and the center of curvature of a mirror is called the **Principal Axis**.

### Final Answer:
The line joining the pole and the center of curvature of a mirror is called the **Principal Axis**.