Which of the following statements is true?

(a) A convex lens has 4 dioptre power having a focal length 0.25 m

(b) A convex lens has –4 dioptre power having a focal length 0.25 m

(c) A concave lens has 4 dioptre power having a focal length 0.25 m

(d) A concave lens has –4 dioptre power having a focal length 0.25 m

 

Answer

sign-convention-for-lens---teachoo2.jpg

 

  • A convex lens has 
    • a positive focal length ( 0.25m) 
    • and hence would also have a positive power (+4D). 
  • A concave lens has 
    • negative focal length (-0.25m) 
    • and hence has negative power ( -4D)


So, the correct answer is (a)

  1. Class 10
  2. Chapter 10 Class 10 - Light - Reflection and Refraction (Term 1)

About the Author

CA Maninder Singh's photo - Founder at Teachoo
CA Maninder Singh
CA Maninder Singh is a Chartered Accountant for the past 11 years and a teacher from the past 11 years. He teaches Science, Accounts and English at Teachoo