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A convex lens of focal length 10 cm is placed coaxially 5cm away from a concave lens of focal length 10cm. If an object is placed 30cm in front of convex lens, find the position of final image formed by combined system.
me getting at ∞
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30 Answers
1u will get the same answer
u=+10
f=-10
v=?
1/f=1/v-1/u
-> 1/(-10)=1/v - 1/10
-> 1/v= -1/10 + 1/10
-> v= infinity!!
9:D i m frustrated that i took a lens as mirror in board exam itself
62sorry guys i added to all the confusion here by pinking that one..
I was for a moment doing the same that celestine did! :(
And I thought why did every one else mess it up :D
1No sky, we got confused as his answer was pinked, now he has deleted it!!
1yes its at ∞ coz the image formed by convex lens acts as a "virtual object" formed at focus of concave lens!!
:-)
9i wonder how i took a concave lens as a concave mirror in the board exam :(
9prateeks method totally right
( the funny part is my very wrong post had been pinked - now ive deleted all those stupid posts of mine )
9oh sorry sorry i am totally wrong kick me as much as u wish
i made a blunder by considering it as a mirror ;(
1yes !! it is lens formula, how u told prateek's mthod is not the correct one!, pls explain
1hey celestine...
its thin lens formula ... not mirror formula (post #18)
1no, i got it as 15 cm on another side of convex lens.., therefore , 10 cm on the side of concave lens... so image at infinity!!
1It is infinity man
It's a very simple question,though I attempted the other option given in question
1IT WILL BE INFINITY ONLY.....
FOR CONVEX LENS...
u=-30 cm
f=10 cm....
FROM LENS FORMULA....v=15 cm....
SINCE THE CONCAVE LENS IS 5 cm away from the lens...and since the focal length of concave lens is 10 cm...the image formed by convex lens is 15 cm away from it....
THEREFORE FOR CONCAVE LENS THE IMAGE FORMED BY THE CONVEX LENS WILL ACT AS AN VIRTUAL OBJECT FOR THE CONCAVE LENS....AND THE LIGHT RAYS WHICH R DIRECTED TOWARDS THE FOCUS OF CONCAVE LENS ARE REFRACTED IN PARALLEL DIRECTION(PARALLEL TO THE PRINCIPAL AXIS) BY THE CONCAVE LENS....
AND HENCE THE IMAGE IS FORMED AT INFINITY.....
1yeah i hav 2wice reslved it it is infinity.
apni feelings ko khud par haavi mat hoone do
