Question

A saving mirror has a radius of curvature of 30cm .A man sees his image 2.5 times the size of his face .How far the mirror from his face.​

Answer 1

Answer: the previous answer is wrong

Explanation:

R =30 cm

F = -30/2 = -15 cm

We know,

Magnification, m = -v/u

=> 2.5 = -v/u

=> -2.5u = v

Now,

1/f = 1/u +1/v

=> -1/15 = 1/u -1/2.5u

=> -1/15 = (2.5-1)/2.5u

=> -1/15 = 1.5/2.5u

=> 2.5u = -15 x 1.5

=> u = -22.5/2.5

=> u = -9

Mirror is 9 cm far from his face.

Hope it helps !!

Answer 2

Answer:

The correct answer of this question is  9 cm.

Explanation:

Given - A saving mirror has a radius of curvature of 30cm. A man sees his image 2.5 times the size of his face.

To Find - How far is the mirror from his face.​

The reflective surface of a concave mirror is curled inward and away from the light source. Light is reflected inward by concave mirrors to a single focus point.

A concave mirror is used as a shaving mirror.

Given =  R =$-30 cm$

m = $2.5$

$f = \frac{R}{2} =-15$

Now, use the $m = - \frac{v}{u}$

$2.5 = - \frac{v}{u}$

$v = -2.5u$

Now, use the mirror formula,

$\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$

$\frac{1}{-15} = \frac{1}{2.5u} + \frac{1}{u}$

$-\frac{1}{15} = \frac{-1}{2.5u} + \frac{2.5}{2.5u}$

$u = - 9$

So, the distance of the face from the mirror is 9 cm.

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