CUSAT 2022 BTech Solved Paper Shift 1

A convex lens is placed 8‌cm from a light source and it makes a sharp image on a screen, kept 8‌cm from the lens. Now a glass block (refractive index 1.5) of 1.2‌cm thickness is placed in contact with the light source. To get the sharp image again, the screen is shifted by a distance d. Then d is