Sapphire has an index of refraction of 1.77. The critical angle for sapphire in air with an index of refraction of 1.0 is degrees.

The  value is  

Explanation:

From the question we are told that

   The  index of refraction is  

   The  refractive index of air is  

Generally the critical angle is mathematically represented as

=>    

=>    

=>    

answer would be letter choice (a),   a ball resting on a shelf. would be another example of potential energy   >   stored energy > not moving.

a ball spinning on a finger   >   kinetic energy > moving energy

a ball rolling on the ground   >   kinetic energy   > moving energy

a   ball flying through the air   > kinetic energy   >   moving energy

hope that                                         : )