Question

The image of an object which is 10cm from a lens is formed on the same side as the object. If the image is 10cm behind the object, Find the focal length of the lens.
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Answer 1

Answer:

Focal length is 6.67 cm.

Explanation:

Object distance, u, from the lens = 10 cm

Image distance, v, to the lens = 10 cm + 10 cm

                                                 =  20 cm

Apply the lens formula to determine the focal length, f, of the lens.

$\frac{1}{f}$ = $\frac{1}{u}$ + $\frac{1}{v}$

 = $\frac{1}{10}$ + $\frac{1}{20}$

    = $\frac{2 + 1}{20}$

$\frac{1}{f}$  = $\frac{3}{20}$

Find the inverse of both sides, so that;

f = $\frac{20}{3}$

  = 6.67

f = 6.67 cm

The focal length of the lens is 6.67 cm.