An air bubble under water shines because of the phenomenon of 

Explanation:

Total Internal Reflection (TIR): 

When the Angle of incidence exceeds the critical angle then light ray comes back into the same medium after reflection from the interface. This phenomenon is called Total internal reflection (TIR). 

Conditions for TIR: 

• The ray must travel from a denser medium to a rarer medium.
• The angle of incidence (i) must be greater than the critical angle C.

Illustrations of Total Internal Reflection

• Sparkling of a diamond.
• Mirage and looming.
• Shining of an air bubble in water.
• Increase in duration of the sun’s visibility.
• Shining of a smoked ball or a metal ball on which lamp stool deposited when dipped in water.
• Optical Fibre.

Applications

• For transmitting optical signals and the two-dimensional picture.
• For transmitting electrical signals by first converting them to light.
• For visualising the internal sites of the body by doctors in endoscopy.