Total Internal Reflection

Refraction Review

• Refraction means bending.

• How does light go through glass anyway?–Does NOT go through!

–Absorbed & Re-emitted countless times.

Glass MoleculesPhoton of light Gulp!

BURP!

Gulp! Gulp!

BURP!

BURP!

BURP!

Gulp!

Total Internal Reflection: Shine a light upwards out of water:• Some light will leave the water,

• Some light will reflect back downwards at an equal angle.

Total Internal Reflection

• At a certain angle...

• Light doesn’t go through the surface of the water anymore!

• Demo...

Critical Angle: Θc

• Occurs when:

• ni > nt and Θi > Θc

“Occurs when:ni > nt and Θi > Θc”

What does this mean?

• ni > nt : • Θi > Θc :

Finding the critical angle:• Sound familiar:

• ni sinΘi = nr sinΘr

• When Θr = 90, TIR occurs.

• sin(90) = ___?• So...........

• sinΘc = nr/ni

• (Does everybody know where the sin-1 button is on their calculators?)

• Know of any technology that uses this principle???

Total Internal Reflection HW

• Read p. 403-405

• Do p. 410 # 10, 11, 16, 22, 23, 50-53