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An object placed 18cm in front of a convex mirror produced an image 6cm behind t...


Question

An object placed 18cm in front of a convex mirror produced an image 6cm behind the mirror. Find the focal length of the mirror.

Options

A) 9.0cm

B) 7.5cm

C) -6.5cm

D) -9.0cm

E) 4.5cm

The correct answer is E.

Explanation:

By mirror formula:
\(\cfrac{1}{f} = \cfrac{1}{u} + \cfrac{1}{v} = \cfrac{1}{18} + \cfrac{1}{6} = \cfrac{1+3}{18} = \cfrac{4}{18}\)
\(f = \cfrac{18}{4}\)
= 4.5cm

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Dicussion (1)

  • By mirror formula:
    \(\cfrac{1}{f} = \cfrac{1}{u} + \cfrac{1}{v} = \cfrac{1}{18} + \cfrac{1}{6} = \cfrac{1+3}{18} = \cfrac{4}{18}\)
    \(f = \cfrac{18}{4}\)
    = 4.5cm

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