Question
A student focuses the image of a well-illuminated distant object on a screen using a convex lens. After that, he gradually moves the object towards the lens and each time focuses its image on the screen by adjusting the lens.
i) In which direction, towards the screen or away from the screen, does he move the lens?
ii) What happens to the size of the image? Does it decrease or increase?
iii) What happens to the image on the screen when he moves the object very close to the lens?
Solution
(i) The image distance increases, when an object is moved towards the lens. Thus, in order to focus the image, the student moves the lens away from the screen.
(ii) The size of the image increases when the object is moved towards the lens.
(iii) When the object is moved very close to the lens, no image is formed on the screen. A virtual image is formed behind the object on the same side of the screen.
(ii) The size of the image increases when the object is moved towards the lens.
(iii) When the object is moved very close to the lens, no image is formed on the screen. A virtual image is formed behind the object on the same side of the screen.
