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Optics

Blazing goIITian

Joined:	4 Jun 2007
Post:	434

20 Apr 2009 22:49:21 IST

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314

simple....

None

a convex lens A of focal length 20cm and a concave lens of focal length 5 cmare kept along the same axis a distance d apart.a parallel beam passing A leaves parallel after passing B....so the distance d is.....

.........ans is b.....why cant it be a????

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Aditya

Hot goIITian

Joined: 13 Sep 2008

Posts: 196

20 Apr 2009 23:00:21 IST

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if the ans is a then the object will be real for concave lens and a virtual image will be formed...

so i think because of this its b....

please rate if useful...and correct if wrong....

vignesh the cooler version of newton

Blazing goIITian

Joined: 16 Mar 2008

Posts: 1801

20 Apr 2009 23:00:32 IST

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answer is surely 15.. because since the resultant beams are parallel, the beam passing thro B must be appearing to converge at its focus...and since the initial beam is parallel, it must converge to the focus of the convex lens..i.e the focus of convex and concave lens must coincide for this to happen.. now, draw the diagram and i'll be clear why it cant be 25..

shubham sunder

Blazing goIITian

Joined: 4 Jun 2007

Posts: 434

21 Apr 2009 00:59:14 IST

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k....yes got my mistake....silly one indeed ,.....thnx for the reply....

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