If the radius of curvature of a concave mirror is 12 cm. what is it's focal length?
Answers
Answer:
focal length f of concave mirror = 1/2 of radius of curvature = 12/2 = 6 cm .
focal length f of concave mirror = 1/2 of radius of curvature = 12/2 = 6 cm .
magnification of mirror, m = -v/u = -1.5 .(1)
where v is image distance and u is object distance
(it is given that image is real. In concave mirror real images are inverted, hence -ve sign i.e. -1.5 is used in eqn.(1) )
from eqn.(1) , v = 1.5 u ..(2)
we have mirror eqn., begin mathsize 12px style
1 over v space plus space 1 over u space equals space 1 over f space. left parenthesis 3 right parenthesis end style
Substituting value of f and using eqn.(2), eqn.
(3) becomes : begin mathsize 12px style fraction numerator 2 over denominator 3 u end fraction plus 1 over u space equals space 1 over 6 space. left parenthesis 4 right parenthesis end style
solving for u in the eqn.(4), we get u = 10 cm