Question

Ray tracing for a flat mirror shows that the image is located a distance behind the mirror equal to the distance of the object from the mirror. This is stated di = –do , since this is a negative image distance (it is a virtual image).

(a) What is the focal length of a flat mirror?
(b) What is its power?

Answer 1

The focal length of a flat mirror is considered to be infinite, and its power is therefore zero diopters.

Step-by-step explanation:

Focal Length and Power of a Flat Mirror

When considering ray tracing for a flat mirror, we can determine that the image formed is virtual and located the same distance behind the mirror as the object is in front of it, represented by the equation di = -do. Now addressing the question:

• (a) What is the focal length of a flat mirror?
• The focal length (f) of a flat mirror is considered to be at infinity because parallel rays reflecting off the mirror do not converge or diverge after reflection. Therefore, using the mirror equation (1/f = 1/do + 1/di), we substitute infinity for the focal length, leading to the conclusion that the focal length of a flat mirror is infinite.
• (b) What is its power?
• The power (P) of a mirror is the reciprocal of its focal length (P = 1/f), measured in diopters (D). Since the focal length of a flat mirror is at infinity, the power of a flat mirror is zero diopters.