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1)The 2 adjacent walls and the ceiling of a rectangular room are mirror surfaced.What is the number of images of himself does an observer sees?

If it was the case of 2 mirrors I know it is 3. But here there are 3 mirrors which are mutually perpendicular. But if we take 2 mirrors at a time then the total number of images is 9. What do you say Sir/Madam?

2)A convergent beam of light is incident on a convex mirror of radius of curvature 60 cm as shown in figure. What is the nature and position of the image formed by it?

I solved it in the following way:

Let u, v and f be the object distance, image distance and focal length of the convex mirror respectively.

Here u = + 10 cm, f = +30 cm

1/u + 1/v = 1/f

v = (uf)/(u-f)

= (10 x 30)/(10 – 30)

= -15 cm

Hence the image formed is virtual and 15 cm in front of the mirror. Is it right?

3)A convex mirror of focal length f produces an image (1/n)th of the size of the object. What is the distance of the object from the mirror?

I solved it in the following way:

Magnification = 1/n = -(v/u)

i.e. v = -(u/n)

1/u + 1/v = 1/f

1/u – (n/u) = 1/f

By solving I get,

u = (1-n)f

Are my sign conventions right? Sometimes the diagram may not be clear. So I will try to describe the diagram. A convergent beam of light serves as a virtual object which appears to converge at a distance of 10 cm behind the mirror.

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# Number of images formed by 3 mutually perpendicular plane mirrors

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