A mark is made on the surface of a glass sphere of diameter 10cm and refractive index 1.5. It is viewed through…..

Q. A mark is made on the surface of a glass sphere of diameter 10cm and refractive index 1.5. It is viewed through the glass from a portion directly opposite. The distance of the image of the mark from the centre of the sphere will be

(a) 15 cm

(b) 17.5 cm

(c) 20 cm

(d) 22.5 cm

Ans: (a)

Sol: μ₂/v -μ₁/u = (μ₂ -μ₁)/R

1/v -1.5/(-10) = (1-1.5)/(-5)

1/v + 3/20 = 1/10

1/v = -3/20 +1/10 = -1/20

v= -20 cm

Hence , Distance from centre = 15 cm