A combination of two thin lenses with focal lengths 
and 
respectively forms an image of distant object at distance 60 cm when lenses are in contact. The position of this image shifts by 30 cm towards the combination when two lenses are separated by 10 cm. The corresponding values of 
and 
are
Text Solution
Verified by ExpertsB
Initially 
(Focal length of combination)
Hence by using 
⇒ ⇒ 
⇒ ⇒ 
......(i)
Finally by using 
where 
and d = 10 cm
⇒ ⇒ 
......(ii)
From equations (i) and (ii) 
From equation (i) 
…..(iii)
Also, difference of focal lengths can written as
⇒ ⇒ 
…..(iv)
From (iii) × × (iv) 
and 
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