Question

An object 2.5 cm high is placed at a distance of 10 cm from a concave mirror of radius of curvature
30 cm, The size of the image is
(1) 9.2 cm
(2) 10.5 cm
(3) 5.6 cm
(4) 7.5 cm
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Answer 1

Answer:

7 is correct answer not 7.5 given in options..

Answer 2

Explanation:

Given- object size,h= 2.5 cm

object distance,u= -10 cm

Radius of curvature,R= -30 cm

we know that-

R= 2f

R/2 = f

-30/2 = f

-15 = f

Therefore,f = -15

v=?

h'=?

By mirror formula-

1/f = 1/v + 1/u

1/v = 1/f - 1/u

1/v = 1/(-15) - 1/(-10)

1/v = 1/(-15) + 1/10

1/v = -2+3/30

1/v = 1/30

so,v= 30

Now, Magnification--

h'/h = -v/u

h' = -v/u × h

h'= -30/-10 × 2.5

h'= 3 × 2.5

Therefore,h' = 7.5 cm

So, the size of the image is 7.5 cm