Anobject is placed at a distance of 10 cm from a coaxial combination of two lenses A and B contact. The combination forms a real image three times the size of an object. If len B is concave with a focal length of 30 cm, what is the nature and focal lenght of lens A ?

Anobject is placed at a distance of 10 cm from a coaxial combination o

1.	Anobject is placed at a distance of 10 cm from a coaxial combination of two lenses A and B contact. The combination forms a real image three times the size of an object. If len B is concave with a focal length of 30 cm, what is the nature and focal lenght of lens A ?
Answer» Convex, 6 cm CONCAVE, 12 cm Convex, 12 cm Convex, 20 cm Solution :(a) Linear magnification (m) `= (v)/(U) = - 3` v = - 3u u = - 10 cm, `therefore v = + 30 cm` `(1)/(F) = (1)/(v) - (1)/(u)` `rArr` Focal LENGTH of combination `(F) = (15)/(2) cm` Focal length of concave lens `(f_(1)) = 30 cm` `therefore "" (1)/(F) = (1)/(f_(1)) + (1)/(f_(2))` `rArr "" f_(2) = + 6 cm`.

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Anobject is placed at a distance of 10 cm from a coaxial combination of two lenses A and B contact. The combination forms a real image three times the size of an object. If len B is concave with a focal length of 30 cm, what is the nature and focal lenght of lens A ?

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