Question Detail

Using the lens formula: 1/f = 1/u + 1/v. u = 13 inches, v = 90 inches. 1/f = 1/13 + 1/90 = (90 + 13) / (13 × 90) = 103 / 1170. f = 1170 / 103 = 11.36 inches. None of the options match. Let's re-read the problem: 'A double-convex lens is used to project a slide. The slide is 2 inches high and 13 inches from the lens. The image is 90 inches from the lens.' The lens formula is 1/f = 1/u + 1/v. If u = 13 in, v = 90 in, f = 11.36 in. Not an option. If the slide is 13 inches from the lens and the image is 90 inches from the lens, the focal length is 11.36 inches. The closest option is 30 inches, which is incorrect. There might be a typo in the question. If the slide is 2 inches high, this is related to magnification, but not needed for focal length.