1
Question
If an object is placed 21 cm from a converging lens, the image formed is slightly smaller than the object. If the object is placed 19 cm from the lens, the image formed is slightly larger than the object. The approximate focal length of the lens is :
(a) 5 cm
(b) 10 cm
(c) 18 cm
(d) 20 cm
If an object is placed 21 cm from a converging lens, the image formed is slightly smaller than the object. If the object is placed 19 cm from the lens, the image formed is slightly larger than the object. The approximate focal length of the lens is :
(a) 5 cm
(b) 10 cm
(c) 18 cm
(d) 20 cm
Open in App
Solution
The correct option is (b) 10 cm
From the question, it is clear that the size of the image is slightly smaller at 21 cm and slightly larger at 19 cm.
Here since the boundary condition(i.e. object and image are of the same size) is between 19 cm and 21 cm hence the answer is 20 cm.
It means that the center of curvature is at 20 cm so the focal length will be at 10 cm.
The correct option is (b) 10 cm
From the question, it is clear that the size of the image is slightly smaller at 21 cm and slightly larger at 19 cm.
Here since the boundary condition(i.e. object and image are of the same size) is between 19 cm and 21 cm hence the answer is 20 cm.
It means that the center of curvature is at 20 cm so the focal length will be at 10 cm.
Suggest Corrections
26
Join BYJU'S Learning Program
Explore more
Join BYJU'S Learning Program
