A ray of light passing through the centre of curvature of a concave mirror is reflected by the mirror at?

1. Analyze the question A ray passes through the centre of curvature (C) of a concave mirror and strikes the mirror. We are asked the angle at which it is reflected.

2. Concept The line from the centre of curvature to any point on the mirror is a radius of the sphere, so it is normal (perpendicular) to the mirror surface at that point.

A ray passing through C therefore travels along the normal, which means:

• Angle of incidence, i = 0° (the angle is measured between the ray and the normal, not the surface)
• By the law of reflection, angle of reflection, r = i = 0°

3. Solution

• The ray travels along the radius, which is the normal, so i = 0°.
• Since r = i, r = 0°.
• The ray is reflected straight back along its original path.

4. Answer The ray is reflected at 0° (angle of reflection measured from the normal).

Note that option D (180°) describes the change in the ray's direction, since it returns along the same path. But the question asks about the angle of reflection, and by the law of reflection that is 0°.

5. Tip Remember: "Through C, the ray goes back the way it came." In JAMB, the angles of incidence and reflection are always measured from the normal, not from the mirror surface. A ray along the normal gives 0°.