The refractive index of glass w.r.t. a medium is `4/3` . If ` V_m-V_g=6.25 xx 10^(7) m//s `, then the velocity of light in the medium will be

Options

A. ` 2.5 xx 10^(8) m//s `
B. `2.25 xx 10^(8) m//s `
C. `1.875 xx10^(8) m//s `
D. `1.5xx10^(8) m//s `

Answer

A

Explanation

`""_(m) n_(g)=(V_(m))/(V_g)=(4)/(3) :. V_m=(4)/(3)V_g`
`:. V_m-V_g=V_g((4)/3-1)=(V_g)/(3)`
`:. (V_g)/(3)=6.25 xx 10^(7)`
`:. V_g=1.875 xx 10^(8) m//s `
`V_m=(4)/(3)V_g=2.5 xx 10^(8) m//s `