What is "critical angle"

Critical \Crit"ic*al\ (kr[i^]t"[i^]*kal), a. [See Critic, n., Crisis.]

1. Qualified to criticise, or pass judgment upon, literary or artistic productions.

   It is submitted to the judgment of more critical ears to direct and determine what is graceful and what is not.
   --Holder.

2. Pertaining to criticism or the critic's art; of the nature of a criticism; accurate; as, critical knowledge; a critical dissertation.

3. Inclined to make nice distinctions, or to exercise careful judgment and selection; exact; nicely judicious.

   Virgil was so critical in the rites of religion, that he would never have brought in such prayers as these, if they had not been agreeable to the Roman customs.
   --Bp. Stillingfleet.

4. Inclined to criticise or find fault; fastidious; captious; censorious; exacting.

   O gentle lady, do not put me to 't, For I am nothing, if not critical.
   --Shak.

5. Characterized by thoroughness and a reference to principles, as becomes a critic; as, a critical analysis of a subject.

6. [See Crisis.] Pertaining to, or indicating, a crisis, turning point, or specially important juncture; important as regards consequences; hence, of doubtful issue; attended with risk; dangerous; as, the critical stage of a fever; a critical situation.

   Our circumstances are indeed critical.
   --Burke.

   The small moment, the exact point, the critical minute, on which every good work so much depends.
   --South.

   Critical angle (Optics), that angle of incidence of a luminous ray at which it is wholly reflected, and no portion of it transmitted. The sine of this angle is the reciprocal of the refractive index of the medium.

   Critical philosophy, the metaphysical system of Kant; -- so called from his most important work, the ``Critique of Pure Reason.''

n. 1 (context physics English) The smallest angle of incidence for which light is totally reflected from a boundary between one medium and a less refractive one 2 (context aerodynamics English) The smallest angle of attack of an airfoil at which lift suddenly decreases and drag suddenly increases 3 (context architecture English) The smallest angle of a ramp or stairs considered uncomfortable or unsafe

n. the smallest angle of incidence for which light is totally reflected

Critical angle can refer to:

• Critical angle (optics); the angle of incidence above which Total Internal Reflection occurs
• Critical angle of attack, in aerodynamics; the angle of attack which produces the maximum lift coefficient
• Critical angle of repose, in engineering; the steepest angle of descent of a slope when the material is on the verge of sliding