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A simple microscope forms an image 10cm from an eye close to the lens. If...

Physics
WAEC 2000

A simple microscope forms an image 10cm from an eye close to the lens. If the object is 6cm from the eye, calculate the focal length of the lens

  • A. 3.75cm
  • B. 4.00cm
  • C. 15.00cm
  • D. 16.00cm
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Correct Answer: Option A
Explanation

Given: u = -6 cm (the object is 6 cm from the eye, and the direction is negative), v = 10 cm (the image is 10 cm from the eye)

Using the lens formula:  \(\frac{1}{\text{f}}\) =  \(\frac{1}{\text{v}}\) -  \(\frac{1}{\text{u}}\)

\(\frac{1}{\text{f}}\) = \(\frac{1}{10}\) +  \(\frac{1}{6}\)

\(\frac{1}{\text{f}}\) =  \(\frac{8}{\text{30}}\)

So that f = 3.75cm upon cross multiplying

Therefore, the focal length of the lens is 3.75 cm.


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