The distance between an object and its real image in a convex lens is 40cm….

The distance between an object and its real image in a convex lens is 40cm. If the magnification of the image is 3, calculate the focal length of the lens

  • A.
    6.5 cm
  • B.
    7.5 cm
  • C.
    8.5 cm
  • D.
    4.5 cm
Correct Answer: Option B
Explanation

u + v = 40

(frac{v}{u}) = 3

v = 3u

u + 3u = 40

4u = 40

u = 10cm

v = 3u = 30cm

f = (frac{uv}{u + v} = frac{10(30)}{10 + 30} = frac{300}{40})

= 7.5 cm

There is an explanation video available below.

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