# physics

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A slide is 5 inches high. it is placed 5.5 inches from the convex lens of a porjection lantern. The image is cast upon a screen 55 inches away. the focal length of the lens is ______inches?
b) the heigh of the image cast by the lens is ________inches?

• physics -

(a) Use the lens formula.
1/5.5 + 1/55 = 1/f
Solve for the focal length, f.
10/55 + 1/55 = 11/55 = 1/5 = 1/f
One more step.

(b) image height = (object height)x(55/5.5)
= 5*10 = ___ inches

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