Radius of curvature of a mirror is +20 cm, it is a :

Options

A. Convex mirror
B. Concave mirror
C. Plane mirror
D. Nothing can be said with certainty

Answer

To determine the type of mirror based on the given radius of curvature, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Radius of Curvature**: The radius of curvature (R) is the distance from the mirror's surface to its center of curvature. It is given as +20 cm.

2. **Identify the Sign Convention**: In optics, the sign convention is crucial. A positive radius of curvature indicates that the center of curvature is located on the same side as the incoming light (the reflective surface).

3. **Determine the Type of Mirror**:
- If the radius of curvature is positive, it indicates that the mirror is a **convex mirror**. This is because, in a convex mirror, the center of curvature is located behind the mirror (on the side opposite to the incoming light).
- Conversely, if the radius of curvature were negative, it would indicate a concave mirror, where the center of curvature is in front of the mirror.

4. **Conclusion**: Since the radius of curvature is +20 cm, the mirror is a **convex mirror**.

5. **Focal Length Calculation**: The focal length (f) of a mirror is related to the radius of curvature by the formula:
\[ f = \frac{R}{2} \]
Substituting R = +20 cm:
\[ f = \frac{20 \text{ cm}}{2} = +10 \text{ cm} \]
This confirms that the focal length is also positive, consistent with a convex mirror.

### Final Answer:
The mirror with a radius of curvature of +20 cm is a **convex mirror**.