Question

A convex lens of focal length 50 cm and a concave lens of focal length 100 cm are separated by a distance of 10 cm. What is the power of the combination?    

Solution

Correct option is

+1.2 D

 

The focal length of the combination is  

                          

Where f1 = +50 cm, f2 = – 100 cm and t = 10 cm. Using these values we get    

Therefore power 

SIMILAR QUESTIONS

Q1

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?

Q2

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?

Q3

The refractive index of a glass prism depends upon 

Q4

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?

Q5

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 

                                                           

Q6

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

Q7

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   

Q8

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)?

Q9

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

Q10

How will the image formed by a convex lens be affected if the central portion of the lens is wrapped in black paper, as shown in fig.