what are conditions for total internal reflection
When light is incident from a denser to rarer medium the ray deviates away from the normal. For a certain angle of incidence (i = ic) the angle of refraction becomes 900. This angle of incidence is called the critical angle. Any ray with incident angle greater than this critical angle will be completely reflected back to the denser medium (see fig). This phenomenon is called Total Internal Reflection.
Thus, the two essential conditions for total internal reflection:
1. Incident ray should travel in denser medium and refracted ray should travel in rarer medium.
2. Angle of incidence (i) should be greater than the critical angle for the pair of media in contact.