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?

Question

b) the heigh of the image cast by the lens is ________inches?

Answer 1

(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