critical angle


: the least angle of incidence at which total reflection takes place

Illustration of critical angle

Illustration of critical angle
  • AOB
  • AO'B'
  • AO''B'' angles of incidence; AOC refracted ray; AO''C'' totally reflected ray; AO'B' critical angle

Example Sentences

Recent Examples on the Web Likewise, in a second experiment, subjects were presented with the image of Kevin either gazing at the tube or gazing away in the opposite direction and asked to report the critical angle of the tube before toppling. Robert Martone, Scientific American, 29 Dec. 2020 The critical angle reported by subjects depended upon whether Kevin was blindfolded. Robert Martone, Scientific American, 29 Dec. 2020 As the airplane approaches that critical angle, the first event is a stall warning in the cockpit. New York Times, 18 Sep. 2019

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'critical angle.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Word History

First Known Use

1829, in the meaning defined above

Time Traveler
The first known use of critical angle was in 1829

Dictionary Entries Near critical angle

Cite this Entry

“Critical angle.” Dictionary, Merriam-Webster, Accessed 7 Dec. 2022.

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