Question

select the correct answer.
under which condition does a light ray striking a concave mirror reflect off parallel to the principal axis?
a. when the incident ray passes from a point anywhere between the center of curvature and the focal point
b. when the incident ray passes through the center of curvature
c. when the incident ray passes through the focal point
d. when the incident ray passes through a point beyond the center of curvature
e. when the incident ray passes through a point anywhere between the focal point and the vertex

Explanation:

To determine when a light ray striking a concave mirror reflects parallel to the principal axis, we use the laws of reflection for concave mirrors:

• A ray passing through the focal point of a concave mirror reflects parallel to the principal axis.
• Let's analyze each option:
• Option A: A ray between the center of curvature and focal point does not reflect parallel to the principal axis.
• Option B: A ray through the center of curvature reflects back along the same path (since it hits the mirror normally), not parallel to the principal axis.
• Option C: A ray through the focal point reflects parallel to the principal axis (this is a key rule for concave mirrors).
• Option D: A ray beyond the center of curvature reflects towards a point between the focal point and center of curvature, not parallel to the principal axis.
• Option E: A ray between the focal point and vertex reflects to a point beyond the center of curvature, not parallel to the principal axis.

Answer:

C. when the incident ray passes through the focal point