Why Can't There Be a Critical Angle When nB/nA Is Greater Than 1?

  • Context: Undergrad 
  • Thread starter Thread starter ZxcvbnM2000
  • Start date Start date
  • Tags Tags
    Angles Law Snell's law
Click For Summary
SUMMARY

The discussion centers on Snell's Law, specifically the conditions under which critical angles can be defined. It is established that a critical angle occurs only when the refractive index ratio (nB/nA) is less than 1, leading to total internal reflection. When nB/nA exceeds 1, the sine of the angle A would exceed 1, which is mathematically impossible. The confusion arises from attempting to apply Snell's Law in scenarios where the refractive indices are inverted, such as comparing glass to air versus water to air.

PREREQUISITES
  • Understanding of Snell's Law and its mathematical formulation
  • Knowledge of refractive indices for common materials (e.g., air, glass, water)
  • Familiarity with the concept of total internal reflection
  • Basic trigonometry, particularly the properties of sine functions
NEXT STEPS
  • Research the derivation and implications of Snell's Law in optics
  • Explore the concept of total internal reflection and its applications in fiber optics
  • Study the refractive indices of various materials and their significance in optical design
  • Learn about the mathematical limits of sine functions and their relevance in physics
USEFUL FOR

Students and professionals in physics, optical engineering, and anyone interested in the principles of light behavior at interfaces between different media.

ZxcvbnM2000
Messages
62
Reaction score
1
Snell's Law of Angles says that : sinA/sinB = nB/nA

but in order to find critical angles B has to be 90° . I understand that in order to have total internal reflection that nB/nA < 1 but why can't there be a CRITICAL angle when nB/nA > 1 ?

sinA would have to be greater than 1 which cannot happen but if i do it separately : glass to air and water to air and say that air-n-water = nwater/nair it is 1.33/1.5 which is true but if i do it in one go it is 1.5 / 1.33 . I must be doing something wrong , because this seems too easy :S
 
Science news on Phys.org
What do you mean by "if i do it in one go"?
 

Similar threads

Solve Snell's Law: Glass Cube Refractive Index = 1.77
  • · Replies 8 ·
Replies
8
Views
6K
Graduate How to compute phase gradient from Snell's law?
  • · Replies 1 ·
Replies
1
Views
3K
Undergrad Snell's Law: Definition, Equations, Refractive Index & Critical Angle
  • · Replies 1 ·
Replies
1
Views
4K
Find Angle of Refraction: Snell's Law Solution
  • · Replies 3 ·
Replies
3
Views
2K
Graduate Snell's Law - complex angle of refraction (need complement )
  • · Replies 11 ·
Replies
11
Views
8K
Maximum critical angle for total reflection?
  • · Replies 5 ·
Replies
5
Views
3K
Diffraction grating problem involving Snell's Law
  • · Replies 3 ·
Replies
3
Views
6K
Refraction using Snell's law - critical angles
  • · Replies 2 ·
Replies
2
Views
2K
Graduate Optics, reflexion over water: why?
  • · Replies 7 ·
Replies
7
Views
2K
Should optical cables be water tight? Geometric optics
  • · Replies 1 ·
Replies
1
Views
2K