A convex lens has different media on its two sides. Its first focal length is 10 cm. An object is placed at a distance of 15 cm from the first principal focus. The lens produces its image on the other side at a distance of 20 cm from the second principal focus. The second focal lenght is :

A convex lens has different media on its two sides. Its first focal le

1.	A convex lens has different media on its two sides. Its first focal length is 10 cm. An object is placed at a distance of 15 cm from the first principal focus. The lens produces its image on the other side at a distance of 20 cm from the second principal focus. The second focal lenght is :
Answer» 30 cm 10 cm 17.5 cm 35 cm Solution :(a) Newton FORMULA for focal LENGTH `X_(1)X_(2) = f_(1)f_(2)` Here `X_(1) = - 15 cm` `X_(2) = + 20 cm` `f_(1) = - 10 cm` `(-15) (+ 20) = (- 10) f_(2)` `f_(2) = + 30 cm`.

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A convex lens has different media on its two sides. Its first focal length is 10 cm. An object is placed at a distance of 15 cm from the first principal focus. The lens produces its image on the other side at a distance of 20 cm from the second principal focus. The second focal lenght is :

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