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# Calculate the distance between the image and 19-cm-focal-length lens.?

Two converging lenses with focal lengths of 45 cm and 19 cm are 15 cm apart. A 3.8cm--tall object is 20cm in front of the 45-cm-focal-length lens.

also, Calculate the image height.

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- PearlsawmeLv 71 decade agoFavorite Answer
Combined focal length is given by

1/f = 1/f1 + 1/f2 -d/ (f1f2)

1/f = 1/45 + 1/19 -15/ (45*19)

f = 17.45 cm

u= 20 cm

1/f = 1/u + 1/v

1/17.45 = 1/20 + 1/v

v = 136.86cm

Magnification m = v/u = 136.8/ 20 = 6.84

Image height = 6.84*3.8 = 26 cm

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