Question

a concave mirror produces 3 times enlarged image of an object placed at 10 cm in front of it. calculate the focal length of the mirror?
magnification will be +ve or -ve and why?

Answer 1

Dear Student

u= - 10cm

m = +3 = -v/u
(​​​​​​​Magnification will be positive as image produced formed is enlarged and inverted, since such a image is formed only when object is placed between P and F of the concave mirror.)

=) v = 30cm

1/f = 1/v + 1/u

=) 1/f = (u + v) / uv

=) 1/f = (-10 + 30)/-300

=20 / -300

=) f= -15cm


Regards