1. (Full rubric) Two lenses are 35 cm apart, as shown in the picture. They are u
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Question
1. (Full rubric) Two lenses are 35 cm apart, as shown in the picture. They are used to form an image of the object shown. Lens one is diverging with a focal length/--70 cm; lens 2 is converging with a focal length of f2-14 cm. a) Find the location of the image from the first lens. b) What is the object distance for the second lens? (Hint: Find the image created by the first lens; use that image as the object for the second lens.) c) What is the image distance for the second lens? d) What is the total magnification of the 2 lens system? 7.0 cm -14 cm- Object Lens 1 Lens 2 24 cm 35 cm Copyrigt 2007 Peason Prenice Hall 2. (Full rubric) Tommy is farsighted with a near point distance of 400 cm. What should be the focal length of the lenses in his reading glasses? What is the refractive power of these lenses? Assume the glasses are placed 2.2 cm in front of his eyes.Explanation / Answer
(A) for first lens,
focal length, f1 = - 7 cm
object distance, p1 = 24 cm
1/f = 1/p + 1/q1
1/(-7) = 1/24 + 1/q1
q1 = -5.42 cm
image is at 5.42 cm from lens 1 and to the left of lens(same side as object)
(B) p2 = 35 + 5.42 = 40.4 cm
(C) f2 = 14 cm
1/14 = 1/40.4 + 1/q2
q2 = 21.4 cm right to the lens 2
(D) m = m1 m2 = (-q1/p1)(-q2/p2)
m = (5.42/24)(-21.4 / 40.4)
m = - 0.12
2. object distance, p = 25 - 2.2 = 22.8 cm
image distance, q = - (400 - 2.2) = - 397.8 cm
1/f =1/p + 1/q
1/f = 1/22.8 - 1/397.8
f = 24.2 cm = 0.242 m
P = 1/f = 1/0.242 = + 4.13 D
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