Define principal focus of a spherical mirror. (b) For what position of the object does a concave mirror form a real

Question

(a) Define principal focus of a spherical mirror.

(b) For what position of the object does a concave mirror form a real, inverted and diminished image of the object? Draw the ray diagram.

(c) An object 4 cm high is placed at a distance
of 6 cm in front of a concave mirror of focal length 12 cm. Find the position of the image formed.

Answer 1

(a) A number of rays parallel to the principal axis after reflection from a concave mirror meet at a point on the principal axis or appear to come from a point after reflection from a convex mirror on the principal axis. This is called principal focus.

(b) When the object is placed beyond C.

(c) f = -12 cm, u = -6 cm, v = ?, h₁ = 4 cm

1/v = 1/f - 1/u

= 1/(-12) - 1/(-6) = -1/12 + 1/6 = 1/12

So, v = 12 cm