Question

The size of image of an object by a mirror is reduced
to (1/3)'d by a mirror having focal length 20 cm. At
what distance has the object been placed from the
mirror? What is the nature of image and the mirror?
Draw ray diagram(s) to explain your answer.​

Answer 1

Answer:

HII!

lets see the answer in cases!1

CASE 1:-  m=-1/3(in case of concave mirror)

f= -20 cm

m= -1/3 =-v/u

v=u/3

1/f= 1/v +1/u .

=> -1/20 = 3/u + 1/ u= 4/u

therefore.,, u = -80 cm.

CASE 2:-

M=+1/3 (IN CASE OF CONVEX MIRROR)

f=+20 cm.

m=+1/3 =-v/u

v=-u/3.

i/f=1/v+1/u.

=> 1/20= -3/4 + 1/4 =-2/4

therefore, u= -40 cm.

hope it helps!!

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Explanation: