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Light Reflection and Refraction
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18/08/2021 1:49 pm
Topic starter
A magnifying lens has a focal length of 100 mm. An object whose size is 16 mm is placed at some distance from the lens so that an image is formed at a distance of 25 cm in front of the lens.
(a) What is the distance between the object and the lens?
(b) Where should the object be placed if the image is to form at infinity?
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18/08/2021 1:53 pm
f = 100 mm
\(h_1\) = 16 mm
v = -25 cm = -250 mm
\(\frac{1}{v}\) - \(\frac{1}{u}\) = \(\frac{1}{f}\)
\(\frac{1}{-250}\) - \(\frac{1}{u}\) = \(\frac{1}{100}\)
\(\frac{1}{u}\) = -\(\frac{7}{500}\)
u = -71.4 mm = -7.14 cm
Distance between object and lens is 7.14 cm.
(b) The object should be placed at the focus so that the image is formed at infinity.
So, u = -100 mm = -10 cm
The object should be placed 10 cm in front of the lens.