You arc asked to design a lens which has a focal length of 5 m as the Objective
ID: 1838148 • Letter: Y
Question
You arc asked to design a lens which has a focal length of 5 m as the Objective of a telescope, lens will be doubly convex, with Radii of equal value but in opposite directions. The lens is to out of Crown glass whose index of refraction is 1.52. What value would you try to make each Radii in order for the telescope to have the proper focusing length? A convex lens of focal length 30 cm has an object whose position is at 50cm. from the lens, a) What is the position and direction of the image produced under these specifications? (calculate and show on drawing to right) Calculate image position and show it on the diagram. A convex lens of focal length 30 cm has an object whose position is at 20cm. from the lens. What is the position and direction of the image produced under these specifications? (calculate and show on drawing to right) Calculate image position and show it on the diagram.Explanation / Answer
Applying lens maker's formula,
1/f = (n - 1) [1/R1 - 1/R2]
1/5 = (1.52 - 1) [ 1/R - 1/-R] = (0.52)(2/R)
R = 0.52 x 2 x 5 = 5.2 .........Ans
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f = 30 cm
p = 50 cm
applying lens equation,
1/f = 1/p + 1/q
1/30 = 1/50 + 1/q
q = 75 cm
Image will be 75 cm on right from the lens.
m = -q/p = -75/50 = -1.5
image will be inverted and 1.5 times in height.
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f = 30 cm
p = 20 cm
applying lens equation,
1/f = 1/p + 1/q
1/30 = 1/20 + 1/q
q = -60 cm
Image will be 60 cm to the left side from the lens.
m = -q/p = 60/50 = 1.2
image will be uright and 1.2 times in height.
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