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 ..........

Convex lens having focal length 25 cm and concave lens having focal le

1.	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 ..........
Answer» 1.5 cm 27 cm 150 cm 15 cm Solution :`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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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 ..........

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