Question

how far should an object be from the pole of a concave mirror of a focal length 20cm to form a real image whose size is 1/5 th of the image of the object.

plz answer fast
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Answer 1

Answer:

The size of image is 1/5th of that of object...

So, I=5*O

f=20cm

I/O=v/u

5*O/O=v/u

5/1=v/u

Therefore,

v=5u

Now, we have to apply the formula

1/f=1/v-1/u

1/f=1/5u-1/u

1/20=1/5u-1/u

On taking LCM...

1/20=(1-5)/5u

1/20= -4/5u

5u= -4*20

5u=-80

u= -80/5

=-16cm

Therefore,

The object should be kept at u which is 16cm(-ve)

Hope it helps...

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