Figure shows three transparent media of refractive indices , ${\mu }_1,{\mu }_2\text{ and }{\mu }_3\text{. }$ A point object O is placed in the medium. If the entire medium on the right of the spherical surface has refractive index ${\mu }_1$, the image forms at O'. If this entire medium has refractive index ${\mu }_3$, the image forms at O". In the situation shown,