The focal lengths of some converging lenses are being measured in a small room. the first lens is 2.00 m from

Question

an illuminated object and projects a clear image onto a screen 20.0 cm from the lens. What is the actual focal length of the lens? What percent error would be incurred by assuming the focal length to be 20.0 cm? The second lens is 2.00 m from an illuminated object and projects a clear image of the object onto a screen 2.00 cm from the lens. What is the actual focal length of the lens? What percent error would be incurred by assuming the focal length to be 2.00 cm?

Answer 1

idk but can u please help me???

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Answer 2

f = focal length

o = object distance

i = image distance

1/f = 1/o + 1/i

Problem 1   o = 2m = 200 cm, i = 20 cm

1/f = 1/200 + 1/20 = 0.005 + 0.05 = 0. 55

f = 1/0.55 = 18.181818... cm

% error = 100[(20 - 18.181818)/20] = 9.09%

Problem 2   o = 2m = 200 cm, i = 2 cm

1/f = 1/200 + 1/2 = 0.005 + 0.5 = 0. 505

f = 1/0.505 = 1.9801... cm

% error = 100[(2 - 1.9801...)/2] = 0.99%