聲音可唔可以全內反射?為什麼?

依我既理解,係"唔可以"架
因為

Total internal reflection only happens when light travels from X to Y.(***the refractive index of X is larger than that of Y!!!)
全內反射只會發生當光由X去Y。
而X的折射率比Y的折射率大。

附加一些sound wave和light的分別給你:

sound waves:
longitudinal waves縱波, mechanical waves機械波
speed in air: about330 ms^-1

light waves:
transverse waves橫波, electromagnetic waves電磁波
speed in air: about3x10^8 ms^-1

Yes, sound wave can also be totally internal reflected when it travels from a dense medium to a less dense one. In fact, total internal reflection can occur in waves of any sort.
A common example for total internal reflection to occur in sound is when sound wave travels from a layer of cold air (of higher sendity) to a layer of hot air (of lower density).