A thin convex lens of focal length 25cm is cut into two pieces 0.5cm above the principal axis. The top part is placed at (0, 0) and an object placed at (-50 cm, 0). Find the coordinates of the image.

                    

Hint: Use the lens formula.

Step 1: Find the position of the object.

If there was no cut, then the object would have been at a height of 0.5 cm from the principal axis OO'.

Step 2: Find the position of the image.

Applying lens formula, we have,
                                            1v-1u=1f
                                       1v=1u+1f=1-50+125=150
                                    v= 50 cm
                       Magnification is, m= vu=-5050=-1
Thus, the image would have been formed at 50 cm from the optical centre and 0.5 cm below the principal axis. Hence, with respect to the X-axis passing through the edge of the cut lens, the coordinates of the image are (50 cm, -1 cm).