The correct option is Behind the mirror.
Explanation
Spherical mirrors are sections of a hollow sphere. The geometric center of this hollow sphere is termed the centre of curvature. The position of this centre relative to the reflecting surface depends on whether the mirror is concave or convex.
Detailed Analysis
- Convex Mirror: In a convex mirror, the reflecting surface bulges outwards towards the incident light. The inner surface is silvered or coated. Consequently, the centre of the sphere (centre of curvature) lies on the side opposite to the reflecting surface. Therefore, it is located behind the mirror.
- Concave Mirror: In contrast, a concave mirror has its reflecting surface curving inwards. The centre of curvature lies in front of the reflecting surface.
- Pole: The pole is the geometric centre of the reflecting surface itself (on the mirror), not the centre of the sphere.
Key Takeaway: For a convex mirror, both the principal focus and the centre of curvature are virtual points located behind the reflecting surface.