Question

the refractive index of diamond is 2.42 what is the meaning of this statement

Answer 1

ʜᴇʀᴇ ɪs ʏᴏᴜʀ ᴀɴsᴡᴇʀ

ʀᴇғʀᴀᴄᴛɪᴠᴇ ɪɴᴅᴇx sʜᴏᴡs ᴛʜᴇ ᴄᴏᴍᴘᴀʀɪsᴏɴ ᴏғ ʟɪɢʜᴛ sᴘᴇᴇᴅs ɪɴ ᴛᴡᴏ ᴍᴇᴅɪᴜᴍs. ʟɪɢʜᴛ ᴍᴀʏ ᴛʀᴀᴠᴇʟ ғʀᴏᴍ ʀᴀʀᴇʀ ᴛᴏ ᴅᴇɴsᴇʀ ᴍᴇᴅɪᴜᴍ ᴏʀ ғʀᴏᴍ ᴅᴇɴsᴇʀ ᴛᴏ ʀᴀʀᴇʀ ᴍᴇᴅɪᴜᴍ. ᴡʜᴇɴ ᴡᴇ sᴀʏ ʀᴇғʀᴀᴄᴛɪᴠᴇ ɪɴᴅᴇx ᴏғ ᴅɪᴀᴍᴏɴᴅ ɪs ., ɪᴛ ᴍᴇᴀɴs ʟɪɢʜᴛ ɪs ᴛʀᴀᴠᴇʟʟɪɴɢ ғʀᴏᴍ ʀᴀʀᴇʀ ᴛᴏ ᴅᴇɴsᴇʀ ᴍᴇᴅɪᴜᴍ, ᴀɴᴅ sᴘᴇᴇᴅ ᴏғ ʟɪɢʜᴛ ɪɴ ᴀɪʀ (ᴠᴀᴄᴜᴜᴍ) ɪs . ᴛɪᴍᴇs ᴛʜᴇ sᴘᴇᴇᴅ ᴏғ ʟɪɢʜᴛ ɪɴ ᴅɪᴀᴍᴏɴᴅ. ᴏɴ ᴛʜᴇ ᴏᴛʜᴇʀ ʜᴀɴᴅ ɪғ ᴛʜᴇ ʟɪɢʜᴛ ᴛʀᴀᴠᴇʟs ғʀᴏᴍ ᴅᴇɴsᴇʀ ᴛᴏ ʀᴀʀᴇʀ ᴍᴇᴅɪᴜᴍ, ᴛʜᴀᴛ ɪs, ғʀᴏᴍ ᴅɪᴀᴍᴏɴᴅ ᴛᴏ ᴀɪʀ ᴛʜᴇ ʀᴇғʀᴀᴄᴛɪᴠᴇ ɪɴᴅᴇx ᴡɪʟʟ ʙᴇ /..

ʙᴇ ʏᴏᴜʀs..........^_^

Answer 2

It means that the ratio of speed of light in Vacuum or Air with respect to Diamond is 2.42.
Please note that it also means it is the ratio of sine of angle of incidence to the sine of engle of refraction. (sin i/sin r)
Hope it helps.
$n_diamond$ = 2.42 = $v_vacuum/air/v_diamond$
Please note that Diamond has the highest refractive index. $\since$ It is the ratio of same quantities, the constant $\sin i/ \sin r$ is a dimensionless constant with no unit. i.e.,
$₁n₂= M⁰L⁰T⁰$