question_answer

A spherical mirror forms an erect image of size\[\frac{\text{1}}{\text{3}}\text{rd}\] of the object size. If the distance between the object and the image is 30 cm, the focal length of the mirror is :

A)  -15cm

B)                                         -30cm                  

C)  + 30 cm               

D)         + 40 cm