Question

an erect image 3 times the size of object is obtained with concave mirror 36cm what is position of objest​

Answer 1

Answer: magnification m  = - v/u = h'/h  = +3

      v = -3 u        actually  u is negative.  Hence v is positive.

      R = -36 cm    =>  f = R/2 = -18 cm , negative for a concave mirror.

      1/v + 1/u = 1/f,   mirror equation

       1/(-3u)  + 1/u = 1/(-18)

       2/(3u)  = -1/18

       

          u = - 12 cm    v = +36 cm 

 the object is placed 12 cm from pole of concave mirror ,  less than the focal length, to have an ERECT magnified image 3 times the object.