Q.

A point object is placed at the centre of a glass sphere of radius 6 cm and refractive index 1.5. The distance of virtual image from the surface is         [2004]

1 6 cm  
2 4 cm  
3 12 cm  
4 9 cm  

Ans.

(1)

Distance of virtual image from the surface = 6 cm.

The rays coming from the point object fall normally on the glass-air interface and hence pass undeviated. Therefore, if we retrace the path of the refracted rays backwards, the image will be formed at the centre only.