Q20 of 38 Page 83

Identify the device used as a spherical mirror or lens in following cases, when the image formed is virtual and erect in each case.

(a) Object is placed between device and its focus, image formed is enlarged and behind it.


(b) Object is placed between the focus and device, image formed is enlarged and on the same side as that of the object.


(c) Object is placed between infinity and device, image formed is diminished and between focus and optical center on the same side as that of the object.


(d) Object is placed between infinity and device, image formed is diminished and between pole and focus, behind it.

(a) The device when Object is placed between device and its focus, image formed is enlarged and behind it. Will be a concave mirror.



(b) Object is placed between the focus and device, image formed is enlarged and on the same side as that of the object, then the device is a convex lens. It can be shown with the following ray diagram:



(c) Object is placed between infinity and device, image formed is diminished and between focus and optical centre on the same side as that of the object, then the device will be a concave lens. The ray diagram is:



(d) Object is placed between infinity and device, image formed is diminished and between pole and focus, behind it, then the device used will be a convex mirror. The ray diagram will be as follows:



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