given below

Asked by PRAMOD | 1st Dec, 2013, 07:47: PM

Expert Answer:

The mirror formula is given by,

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

Given that,

f = focal length = -20cm

v = image distance

u = object distance

we will assume that the following is given

hi = 3ho

or

h/ ho = 3

hi = image height

h= object height

now as

Magnification = h/ ho = -v/u = 3

we get

v = -3u

 

so, using this in eq. (1), we get

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

or

-1/20 = 2 / 3u

or

u = -13.33 cm

thus, the object distance / position of the object will be

u = -13.33 cm

Answered by Komal Parmar | 2nd Dec, 2013, 12:53: AM

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