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

JEE Main & Advanced Physics Ray Optics Question Bank Critical Thinking

  • question_answer
    A convex lens of focal length 30 cm and a concave lens of 10 cm focal length are placed so as to have the same axis. If a parallel beam of light falling on convex lens leaves concave lens as a parallel beam, then the distance between two lenses will be

    A)            40 cm                                      

    B)            30 cm

    C)            20 cm                                      

    D)            10 cm

    Correct Answer: C

    Solution :

                       Let distance between lenses be\[x\]. As per the given condition, combination behaves as a plane glass plate, having focal length\[\infty \]. So by using \[\frac{1}{F}=\frac{1}{{{f}_{1}}}+\frac{1}{{{f}_{2}}}-\frac{x}{{{f}_{1}}{{f}_{2}}}\] \[\Rightarrow \] \[\frac{1}{\infty }=\frac{1}{+30}+\frac{1}{-10}-\frac{x}{(+30)(-10)}\Rightarrow x=20\]\[cm\]


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