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Class 10
Solutions to CBSE Sample Paper - Science Class 10

If the power of a lens is - 4.0 D, then it means that the lens is a 

(A) concave lens of focal length -50 m 

(B) convex lens of focal length +50 cm 

(C) concave lens of focal length -25 cm 

(D) convex lens of focal length -25 m 

 

Answer - 

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So, the correct answer is (c)  

 

 


Transcript

Question 39 If the power of a lens is − 4.0 D, then it means that the lens is a (A) concave lens of focal length −50 m (B) convex lens of focal length +50 cm (C) concave lens of focal length −25 cm (D) convex lens of focal length −25 m Now, Power of lens = 𝟏/𝒇 Here, focal length is in meter Since Power = −4D 𝟏/𝒇 = −4 (−1)/𝑓 = f f = (−1)/4 m Converting in cm f = (−1)/4 × 100 cm f = −25 cm Since focal length is negative ∴ it is a concave lens So, the correct answer is (C)

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CA Maninder Singh is a Chartered Accountant for the past 12 years and a teacher from the past 16 years. He teaches Science, Accounts and English at Teachoo