Derivation of Spherical Mirror Formula
Introduction
Spherical mirrors are one of the most important optical devices in our daily life. A spherical mirror is a mirror that has a curved surface, and depending on the surface curvature, it can be either a concave or a convex mirror. The formula for spherical mirrors is used to calculate the position, size, and nature of the image formed by a spherical mirror.
Derivation
Let us consider a spherical mirror, such that the radius of curvature of the mirror is R. A point object O is placed at a distance u from the mirror, and its image is formed at a distance v from the mirror, as shown in the figure below:
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According to the laws of reflection, the angle of incidence (i) is equal to the angle of reflection (r).
From the diagram above, we have:
i = angle of incidence = angle AOB
r = angle of reflection = angle COB
Also, from the geometry of the figure above, we have:
angle AOB + angle COB = angle AOC = 90 degrees
Therefore, we can write:
i + r = 90 degrees
Using the mirror formula, we can write:
1/v + 1/u = 1/f
where f is the focal length of the mirror.
From the geometry of the figure above, we have:
AB = u
BC = v
OC = R/2
Using the mirror formula, we can write:
1/v + 1/u = 1/f
1/v + 1/u = 1/R - 1/u
1/v = 1/R - 1/u
1/f = 2/R
f = R/2
Conclusion
The formula for spherical mirrors is given by:
1/f = 1/v - 1/u
where f is the focal length of the mirror, v is the distance of the image from the mirror, and u is the distance of the object from the mirror. This formula can be used to calculate the position, size, and nature of the image formed by a spherical mirror.