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25/09/2021 5:51 pm
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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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25/09/2021 5:54 pm
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.