Question

the refractive index of rock salt is 1.54. what is meant by this statement

Answer 1

Absolute Refractive index =n=Speed of light in vacuum/Speed of light in medium

n=C/V

So The refractive index of Rock salt is 1.54 That means
1.54=Speed of light in vacuum/Speed of light in Rock salt

So, Speed  of light in Rock salt is 1/1.54 times speed of light in vacuum.
Therefor Speed of light in Rock salt is  less [1.94 x 10⁸m/s ] compared to speed of light in vacuum =C = 3 x 10⁸ m/s.

Answer 2

$Answer$

$absolute \: refractive \: index \{of \: rock \: salt \} \: = 1.54 \:$

According to Formula :-

Absolute refractive index = speed of light in vacuum/speed of light in given medium

=> Absolute refractive index = 3×10⁸ (m/s) / 1.54

=> Absolute refractive index × 1.54 = 3×10⁸ (m/s)

=> Absolute refractive index = 3×10⁸ × 1.54

It show that light travels 1.54 times faster in vacuum than in rock salt.