2. Questions Bank
  3. JEE Main & Advanced
  4. Physics
  5. Ray Optics

JEE Main & Advanced Physics Ray Optics Question Bank Refraction at Curved Surface

  • question_answer
    Two thin lenses of focal lengths 20 cm and 25 cm are placed in contact convex. The effective power of the combination is  [CBSE PMT 1990; RPMT 2001]

    A)            45 dioptres                            

    B)            9 dioptres

    C)            1/9 dioptre                            

    D)            6 dioptres

    Correct Answer: B

    Solution :

                       \[\frac{1}{F}=\frac{1}{{{f}_{1}}}+\frac{1}{{{f}_{2}}}=\frac{1}{20}+\frac{1}{25}\]\[\Rightarrow \]\[F=\frac{100}{9}\]\[cm=\frac{1}{9}\]\[metre\]            \[\therefore \] \[P=\frac{1}{1/9}D=9D\]


You need to login to perform this action.
You will be redirected in 3 sec spinner