Angle of incidence and angle of refraction
Angle of incidence is the angle between a ray incident on a surface and the normal line.
To remember a "Ray Incident" use the mnemonic.
Remember the "incident" started here. This will help you remember that the ray of light has to start when an incident occurs.
The angle of refraction is just the opposite of the angle of incidence, that is:
The angle of refraction is the angle between the refracted ray and the normal line.
If light travelling through air has an angle of incidence of 40° then:
Angle of incidence of air 40° - Water angle of refraction 29°
Angle of incidence of air 40° - Glass angle of refraction 25°