Question

please refer this attachment ,I want an accurate answer from this question with step by step method explaination.So no unneccessary rubbish meeting LINKS to be posted or any answer which is not relevant to this...Please understand my situation.I have board exams after a week or after....

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Answer 1

Answer :

option (a) 75 cm

Step-by-step explanation:

Given :-

1) u = -25 cm

2) magnification of erect (so virtual) image as 1.5

now, m = +1.5 (positive because image is virtual)

so, -v/u = +1.5

so, -v/-25 = +1.5

so, v = 1.5 × 25 = 37.5 cm

We now have u and v, so we can find f

using mirror formula,

1/f = 1/v + 1/u

1/f = 1/37.5 + 1/(-25)

1/f = 2/75 - 3/75

1/f = -1/75

f = -75 cm

So, correct option is a) 75 cm

note : it would actually be -75 since focal length of concave mirror is always negative but out of options, 75 is most appropriate.

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Answer 2

Answer:

(a) 75 cm

Explanation:

In concave shaving mirror, virtual erect and large size image, behind the mirror is obtained, using

m = - v/u ⇒ 1.5 = - v/ -25

⇒ v = 75/2 cm

Now, from mirror formula,

1/f = 1/v + 1/u = 1/75/2 + 1/-25

= - 1/75

∴ f = -75 cm

Hence, focal length of concave mirror is 75 cm.

Hope it helps

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