A point object is placed at the center of a glass sphere of radius 6 cm and refractive index 1.5. The distance of the virtual image from the surface of the sphere is
Using refraction formula 1μ2−1R=1μ2v−1u
in given case, medium (1) is glass and (2) is air
So gμa−1R=gμav−1u⇒11.5−1−6=11.5v−1−6
⇒1−1.5−6=1v+1.56⇒0.5v=1v+14
⇒1v=112−14=−212=−16⇒v=6 cm.