Question

In displacement method, there are two position of lens for which we get clear image. First position of the lens is at 40 cm from object and second is at 80 cm, the focal length of lens is (1) 40 cm (2) 40/3 cm (3) 80 cm (4) 80/3 cm

Answer 1

Answer:

 

Explanation:

Answer 2

Answer:

Let us assume that the image formation of the first lens takes place at the screen which is 'x' cm away. For second lens: Object distance i.e. u from the screen is -80 cm and again the image formation i.e. v is 'x - 40' cm. Therefore, the focal length of the lens is 80/3 cm