We learned about Concave and Convex mirrors in the last post
But:
Did you know that Concave and Convex Mirrors are a part of a sphere?
For these mirrors, we have some important terms like
- Center of Curvature
- Radius of curvature
- Pole of the Mirror
- Principal Axis
- Focus of the mirror
Let's look at them one by one
Center of Curvature (C)
We can say that the mirror is a part of the hollow sphere
The center of this sphere is the Center of Curvature
It is represented by the letter C
Note: - Center of curvature of Concave mirror is on the front, and of convex mirror is on the back
Radius of Curvature
The radius of the hollow sphere which the mirror is a part of is the Radius of Curvature
It is represented by the letter R
Note : - that R = PC
Pole of a Mirror(P)
Center of the spherical mirror is called Pole
It is represented by the letter P
Principal Axis
A straight horizontal line passing through pole and center of curvature
Principal focus
For principal focus, let's look at Concave and Convex Mirrors separately
Principal Focus (F) of concave mirror
The point at which
rays parallel to principal axis
coming from infinity converge
after being reflected from concave mirror
is called the principal focus of concave mirror.
Principal Focus (F) of convex mirror
The point at which
rays parallel to principal axis
coming from infinity appear to converge
after being reflected from convex mirror
is called the principal focus of convex mirror.
Note: - Focus of convex mirror is behind the mirror, so it is a virtual focus
Focal Length
It is distance between Pole (P) and Principal Focus (F)
It is represented by the letter f (small letter f)
Relationship between Radius of Curvature and Focal Length Of Spherical Mirror
The focal length is equal to half of the radius of curvature, for any spherical mirror.
Hence
Focal length = Radius of curvature / 2
f = R/2
Questions
Question 1 Page 168 - Define the principal focus of a concave mirror.
Question 2 Page 168 - The radius of curvature of a spherical mirror is 20 cm. What is its focal length?
