Question

A concave mirror is placed on a horizontal table with its axis directed vertically upwards. Let O be the pole and C the center of curvature of mirror. A point object is placed at C. The mirror forms its real image, also located at C. The mirror is now filled completely with water. The image, now, would be

(1) real and remains at C

(2) real and located between C and ∞

(3) virtual and located at a point between C and O

(4) real and located between C and O

Answer 1

(4) real and located between C and O

Fig.(a) shows image at C due to reflection from concave mirror. The ray CP, is, therefore, incident normally on mirror. 

When mirror is filled with water; the incident ray CA first undergoes refraction at water. The refracted ray AB is incident on mirror. This ray is not incident normally. It undergoes reflection obeying law of reflection. The reflected ray again undergoes refraction at water surface forming its real image I that lies between C and O.