A student focused the image of a distant object using a device 'X' on a while screen 'S' as shown in the figure. If the distance of the screen from the device is 40 cm, select the correct statement about the device
The device X is a convex lens of focal length 40 cm.
As the light rays are passing through the device X and the image formed is real thus the given device is a convex lens. Secondly, we are getting a focused image at the screen so the focus length of the lens is 40 cm.