Q. 85.0( 1 Vote )

A convex lens A of focal length 20 cm and a concave lens B of focal length 5 cm are kept along the same axis with a distance d between them. If a parallel beam of light falling on A leaves B as a parallel beam, then the distance d in cm will be
A. 25

B. 15

C. 30

D. 50

Answer :

According to the question following is the ray diagram.


As the incident ray is parallel to the principal axis. Therefore in absence of concave lens it will form an image at focus of convex lens.


v = 20cm = f


Distance of Image I from the concave lens B will be = u = 20 – d


Now, the image I will act as object for the concave lens.


Since image object (image I) is at focus of concave lens. Therefore, Image will be formed at infinity


v =


Focal length = -5cm.


By Lens Formula.






20 – d = 5


d = 20 – 5 = 15cm.


Therefore, the distance d will be 15cm. Hence the option B is correct.

Rate this question :

How useful is this solution?
We strive to provide quality solutions. Please rate us to serve you better.
Related Videos
Foundation | NTSE Most Challenging NumericalsFoundation | NTSE Most Challenging NumericalsFoundation | NTSE Most Challenging Numericals37 mins
Introduction to Spherical LensIntroduction to Spherical LensIntroduction to Spherical Lens42 mins
NCERT | Light- Reflection and Refraction (Part -1)NCERT | Light- Reflection and Refraction (Part -1)NCERT | Light- Reflection and Refraction (Part -1)37 mins
Foundation | How to Solve Numericals on Mirror FormulaFoundation | How to Solve Numericals on Mirror FormulaFoundation | How to Solve Numericals on Mirror Formula58 mins
NCERT | Power of a LensNCERT | Power of a LensNCERT | Power of a Lens31 mins
MTG | Part - 1 (Reflection and Refrection)MTG | Part - 1 (Reflection and Refrection)MTG | Part - 1 (Reflection and Refrection)50 mins
Foundation | Total Internal ReflectionFoundation | Total Internal ReflectionFoundation | Total Internal Reflection35 mins
Quiz | Introduction to LightQuiz | Introduction to LightQuiz | Introduction to Light55 mins
Rapid Fire Quiz on Reflection and RefractionRapid Fire Quiz on Reflection and RefractionRapid Fire Quiz on Reflection and Refraction49 mins
What is Refraction?What is Refraction?What is Refraction?45 mins
Try our Mini CourseMaster Important Topics in 7 DaysLearn from IITians, NITians, Doctors & Academic Experts
Dedicated counsellor for each student
24X7 Doubt Resolution
Daily Report Card
Detailed Performance Evaluation
caricature
view all courses
RELATED QUESTIONS :