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Convex lens having focal length 25 cm an...

Convex lens having focal length 25 cm and concave lens having focal length 30 cm are kept in contact, such that they have the same principal axis. Focal length of this combination is ..........

A

1.5 cm

B

27 cm

C

150 cm

D

15 cm

Text Solution

Verified by Experts

The correct Answer is:
A, C
`1/f=(1)/(f_1)+(1)/(f_2)`
`=(1)/(25)-(1)/(30)(because`For concave `f_2` is negative)
`thereforef=(-(30)(25))/(-30+25)=(-750)/(-5)=150` cm
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