Thin lenses A and B have focal lengths of 6.17 cm and 28.9 cm respectively. A 5.

Question

Thin lenses A and B have focal lengths of 6.17 cm and 28.9 cm respectively. A 5.51 mm high insect is positioned 10.5 cm in front of lens A. Lens B is positioned 58.3 cm on the other side of lens A on a common axis.

Is the ultimate image real or virtual?

Find the position of the final image relative to lens B as a positive number.

Determine the height of the image, also as a positive number.

Is the final image upright or inverted relative to the original?

Thin lenses A and B have focal lengths of 6.17 cm and 28.9 cm respectively. A 5.51 mm high insect is positioned 10.5 cm in front of lens A. Lens Bis positioned 58.3 cm on the other side of lens A on a common axis. ls the ultimate image real or virtual? O Virtual O Real Find the position of the final image relative to lens B as a positive number. Number cm Determine the height of the image, also as a positive number. Number mm s the final image upright or inverted relative to the original? O Upright O Inverted A O Previous Check Answer Next Ext Hint

Explanation / Answer

Part a

For first lens as the object lies between center of curvature and focus hence the image will be beyond center of curvature and it will be real and inverted. That means it will be at a distance 58.3 – 12.34 = 45.96 cm from the second lens. Clearly again this lies between center of curvature and focus hence the image will be beyond center of curvature and it will be real and inverted. So the final image is real.

Part b

As effective focal length of the combination is given by

1/f = 1/f1 + 1/f2 – d/f1f2

And comes out to be f = 7.676 cm

And hence using lens formula, 1/v -1/u = 1/f, v = 28.5 cm.

Part c

As magnification, m = v/u = 2.714

So image height = m*object height = 14.96 mm

Part d

As clear from the discussion in part a, final image is upright.

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