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Find the distance of object from a concave mirror of focal length 10 cm so that image size is four time the size of the object. |
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Answer» Solution :Concave mirror can form real as well as VIRTUAL IMAGE. Here nature of image is not given in the question. So, we will consider two POSSIBLE cases. CaseI (When image is real) Real image is formed on the same side of the object, i.e.u,v and f all are negative. So let, u=-x then, v=-4X as `abs(v/u)=abs(m)=4` and f=-10 cm Substituting in, `1/v+1/u=1/f` We have `1/(-4x)-1/x=1/(-10)OR5/(4x)=1/10` x=12.5 cm Note `absxgtabsf` and we know that in case of a concave mirror, image is real when object lies beyond F case II (When image is virtual) In case of a mirror image is virtual when it is formed behined the mirror, i.e., u and f are negative while v is positive. So let, u=-y then, v=+4y and f=-10cm Substituting in, `1/v+1/u=1/f` we have, `1/(4y)-1/y=1/(-10)` or `3/(4y)=1/10ory=7.5 cm` Note Here `absyltabsf` as we know that image is virtual when the object lies between F and P. |
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