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Find the focal length of a lens of power -2.0 D. What type of lens is this?

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Find the focal length of a lens of power -2.0 D. What type of lens is this?

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Given: P = -2.0 D, f = ?

Applying the formula P = \(\frac{1}{f(m)}\),

we get

-2 = \(\frac{1}{f}\)

⇒ f = \(\frac{1}{-2}\) = -0.5 m = -50 cm

∴ Focal length of the lens is 50 cm.

Negative sign shows that the lens is concave.

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