A convex lens is put 10 cm from a light source and it makes a sharp image on a screen, kept 10 cm from the lens. Now a glass block (refractive index…

A convex lens is put $\displaystyle 10$ cm from a light source and it makes a sharp image on a screen, kept $\displaystyle 10$ cm from the lens. Now a glass block (refractive index $\displaystyle 1.5$ ) of $\displaystyle 1.5$ cm 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 :