Question

an object is placed at 18cm in front of a spherical mirror if the image formed at 4cm to the right of the mirror calculate its focal length is the mirror convex or concave what is the nature of the image what is the radius of curvature of the mirror

Answer 1

1/f=1/u+1/v
1/f=1/(-18)+1/(+4)
1/f=-2+9/36
f=36/7
R=2f
m=-v/u
f=+ve so mirror is convex

Answer 2

u = - 18 cm

v = 4 cm

1 / f = 1 / v + 1 / u

1 / f = 1 / 4 + 1 / (- 18)

1 / f = 1 / 4 - 1 / 1 8

1 / f = 9 - 2 / 36 = 7 / 36

f = 36 / 7 cm

focal length is positive so mirror is convex.

R = 2 × 36 / 7

= 72 / 7 cm