Answer :

(a) Let F be the focal length of the given concavo-convex lens.


Then,


--------------- (i)



The value of can be obtained by using lens makers’ formula:





Substituting these values in equation (i):



F=


For the image to be informed at the same point as the object


u = 2F = 2 x 7.5 = 15 cm.


Therefore, the pin should be placed at a distance of 15 cm from the lens.


(b) If the concave part is filled with water;


If is the focal length of lens in water, the focal length F’ of this combination is given by:



----------------------- (ii)



The value of is calculated by Lens makers’ formula:





Substituting these values in equation (ii):




u’ = 2F= 2× = cm


Displacement of pin = u-u’ = (towards the lens).


Rate this question :

How useful is this solution?
We strive to provide quality solutions. Please rate us to serve you better.
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 :

Lenses are constrHC Verma - Concepts of Physics Part 1

Consider the situHC Verma - Concepts of Physics Part 1

A mass m = 50 HC Verma - Concepts of Physics Part 1

The focal length HC Verma - Concepts of Physics Part 1

A ball is kept atHC Verma - Concepts of Physics Part 1

A 5 mm high pin pHC Verma - Concepts of Physics Part 1

Consider the situHC Verma - Concepts of Physics Part 1

A converging lensHC Verma - Concepts of Physics Part 1

A converging lensHC Verma - Concepts of Physics Part 1

An extended objecHC Verma - Concepts of Physics Part 1