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Hot goIITian

Joined:	7 Mar 2008
Post:	157

13 Apr 2008 08:34:11 IST

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323

Calculate - u.......

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Que. - An object is kept at a distance from lens of power 10D which forms a virtual image at distance of 5cm from the lens. Calculate the distance at which the object is placed.

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Blazing goIITian

Joined: 1 Apr 2007

Posts: 1084

13 Apr 2008 09:48:03 IST

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given power = 10D ..
so focal length becomes 10cm..

now it can either be convex or concave...so take focal length
.... +/-10..

now apply lens formula ...

Karan Singh

Blazing goIITian

Joined: 19 Mar 2007

Posts: 384

13 Apr 2008 11:12:24 IST

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answer is -10/3 for convex lens and -5 for concave lens

Karan Singh

Blazing goIITian

Joined: 19 Mar 2007

Posts: 384

13 Apr 2008 11:40:11 IST

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| P | = 10 D
P = 10 ( convex ) or P = -10 ( concave )

P = 1/f

f = 1/10 m = 10 cm (convex)
OR f= 1/-10m = -10cm (concave)

convex lens
------------------
mirror formula
u is unknown
v = -5 ( its a lens )
f = 10

u = -10/3

concave lens
----------------
mirror formula
u is unknown
v = -5 ( its a lens )
f = -10

u = -5

thats the answer

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