A Convex Glass Lens (μg = 1.5) Has A Focal Length Of 8 Cm When Placed In Air. What Is The Focal Length Of The Lens When It Is Immersed In Water (μw = 4/3)?

Why Kaysons ?

Video lectures

Access over 500+ hours of video lectures 24*7, covering complete syllabus for JEE preparation.

Online Support

Practice over 30000+ questions starting from basic level to JEE advance level.

Live Doubt Clearing Session

Ask your doubts live everyday Join our live doubt clearing session conducted by our experts.

National Mock Tests

Give tests to analyze your progress and evaluate where you stand in terms of your JEE preparation.

Organized Learning

Proper planning to complete syllabus is the key to get a decent rank in JEE.

Test Series/Daily assignments

Give tests to analyze your progress and evaluate where you stand in terms of your JEE preparation.



A convex glass lens (μg = 1.5) has a focal length of 8 cm when placed in air. What is the focal length of the lens when it is immersed in water (μw = 4/3)?


Correct option is

32 cm




Dividing we have






The sun’s disc subtends an angle of 10–2 rad at the earth. What must be radius of curvature of the mirror which will produce on a screen an image of the sun 2 cm in diameter? 


A small strip of plane mirror A is set with its plane normal to the principal axis of a convex mirror B and placed 15 cm in front of B which it partly covers. An object is placed 30 cm from A and the two virtual images formed by reflection in A and B concide without parallax. Find the radius of curvature of B  


A concave mirror (focal length 15 cm) and a convex mirror (focal length 10 cm) are placed co-axially 70 cm apart facing each other. A 2 cm tall object is placed perpendicular to the common axis 20 cm from the concave mirror. How far from the convex mirror is the final image formed by two reflections, first at concave mirror and then at convex mirror?


A motor car is fitted with a convex driving mirror of focal length 20 cm. A second motor car 2.1 m broad and 1.05 m high is 4 m behind the first car. What is the size of the image of the second car as seen in the mirror of the first?


The refractive index of a glass prism depends upon 


A prism of refractive index of  has a refracting angle of 60o. At what angle must a ray be incident on it so that it suffers a minimum deviation?


A ray of light in a medium of refractive index μ1 is partly reflected and refracted at the boundary of a medium of refractive index μ2, as shown in fig. If BOC = 90o. The value of angle i is given by 



A rectangular block of glass of refractive index μ and thickness d is placed over an ink dot made on a pice of paper lying on a table. When viewed from above, the dot will appear to be raised by an amount given by


Two transparent media A and B are separated by a plane boundary. The speed of light in medium A is  and in medium B  The critical angle for which a ray of light going from A toB is totally internally reflected is   


A plano-concave lens is made of glass of refractive index 1.5 and the radius of curvature of the curved face is 50 cm. The power of the lens is