Question

If a convex lens of focal length 75 cm and a concave lens of focal length 50 cm are combined together, What will be their resulting power?​

Answer 1

Answer:

100/75-100/50= -0.666

Answer 2

Resulting power of the combination will be -0.666 D

Explanation:

• Power is defined as the ability of rays to diverge and converge after passing through the lens and given as reciprocal of focal length of lens

             $Power = \frac{1}{focal length (m)}$

• unit of power of lens is dioptre (D)
• When combination of lenses are used then power is given as

                        P = P₁ +P₂ +P₃ +.........

Given,

focal length of convex lens = 75 cm =0.75 m

focal length of concave lens = -50 cm = -0.50 m

Power of combination is given as

=> P = P₁ +P₂

=> P = $\frac{100}{f_{1} } +\frac{100}{f_{2} }$

=> P = $\frac{100}{75 } +\frac{100}{-50 }$

=> P = $\frac{4-6}{3}$

=> P = $\frac{-2}{3}$

=> P = -0.666 D (diopter)

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