A point object at 15cm from a concave mirror of radius of curvature 20cm is made it oscillate along the principal axis with amplitude 2mm. The amplitude of its image will be

according to mirror formula115+1v=220=110      solving v=30  then magnification m= vu=3015=2   this is transverse magnification longitudinal magnification dvdu=-v2u2= m2 =4 so amplitude of image oscillation is 2x4=8