Homework Help

An object is placed 20 cm in front of a converging lens of focal length 10 cm. Find the...

user profile pic

carlos485 | Student, Undergraduate | Honors

Posted April 20, 2012 at 2:07 PM via web

dislike 0 like

An object is placed 20 cm in front of a converging lens of focal length 10 cm. Find the image distance.

1 Answer | Add Yours

user profile pic

justaguide | College Teacher | (Level 2) Distinguished Educator

Posted April 20, 2012 at 2:41 PM (Answer #1)

dislike 0 like

For a lens the relation between object distance, image distance and the focal length is given by 1/Do + 1/Di = 1/f, where Do is the object distance, Di is the image distance and f is the focal length. For a converging lens the focal length is taken to be positive.

As the focal length of the converging lens is 10 cm and the the object is placed at a distance of 20 cm in front of the lens, Do = 20 and f = 10. Using the relation provided earlier:

1/20 + 1/Di = 1/10

=> 1/Di = 1/10 - 1/20 = 1/20

=> Di = 20 cm

The image is formed at a distance of 20 cm from the lens on the side opposite to that where the object is placed.

Sources:

Join to answer this question

Join a community of thousands of dedicated teachers and students.

Join eNotes