The radius of curvature of a concave mirror is 30 cm. Following C
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The radius of curvature of a concave mirror is 30 cm. Following Cartesian Sign Convention, its focal length is expressed as ________.
A. + 30 cm
B. + 15 cm
C. – 30 cm
D. – 15 cm
Please scroll down to see the correct answer and solution guide.
Right Answer is: D
SOLUTION
CONCEPT:
Concave mirror:
- If the inner surface of the spherical mirror is the reflecting surface, then it is called a concave mirror. It is also called a focusing mirror/converging mirror.
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- The size of the image produced by these mirrors can be larger or smaller than the object, depending upon the distance of the object from the mirror.
- The concave mirror can form both real as well as virtual images of any object.
Sign convention in mirrors
- All distance are measured from the pole of the mirror.
- The distance measured from the pole (p) to the left side of the mirror is taken as negative.
- The distance measured from the pole (p) to the right side of the mirror is taken as positive.
- The heights measured upwards and perpendicular to the principal axis of the mirror is taken as positive.
- The heights measured downwards and perpendicular to the principal axis of the mirror is taken as negative.
EXPLANATION:
Given - Radius of curvature (R) = - 30 cm
- The relationship between the focal length (f) and the radius of curvature (R) is given by -
\(\Rightarrow f = \frac{R}{2}\)
\(\Rightarrow f = \frac{-30}{2}=-15 cm\)