When two lenses are used in combination, the first one forms an image that then

Question

When two lenses are used in combination, the first one forms an image that then serves as the object for the second lens. The magnification of the combination is the ratio of the height of the final image to the height of the object. A 1.70 cm -tall object is 54.0 cm to the left of a converging lens of focal length 40.0 cm . A second converging lens, this one having a focal length of 60.0 cm , is located 300 cm to the right of the first lens along the same optic axis.

Find the location and height of the image (call it ) formed by the lens with a focal length of 40.0 cm.

Explanation / Answer

You should have been able to do part a) It is a standard lens formula. ( So Si = f^2 or 1/Do + 1/Di = 1/f) So find the position of the object pretending that the second lens isn't there. Is it real or virtual and how big is it. Now this becomes the object for the second lens. using So Si = f^2 we get that Si = 1700/17 = 100 and the distance from the lens is 140 cm the magnification is Di / Do = 140 / 54 = 2.59 and as the object is outside the focal length it is a real image.

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