Optics: Fundamental Laws of Geometric Optics (Part 3; Exam 1)

What is the critical angle?

*Tipping point;

The specific angle of incidence where light hitting a boundary turns into a 90-degree angle of refraction.

Why is the critical angle called the tipping point?

Because it is where light stops passing through and instead reflects entirely back inside.

What is total internal reflection?

Where light traveling through a dense medium hits a boundary and reflects 100% back into the material instead of passing through.

What is a mirage?

A naturally occurring optical phenomenon in which light rays bend via refraction to produce a displaced image of distant objects or the sky.

What is the principle of reversibility?

States that light rays will precisely retrace their exact path in reverse if their direction is inverted.

What is the Abbe number?

A measure of how much a transparent material disperses, or splits light into different colors.

What does a high Abbe number indicate?

Low dispersion. SMALLER dispersion of material.

All colors of light bend at nearly the same angle, which reduces color blur or rainbow fringing.

What does a low Abbe number mean?

High dispersion. Colors bend at different angles, creating noticeable color dispersion.

What color light bends the BEST?

BLUE!

How is the Abbe number calculated?

Using the refractive index (how much light bends) at THREE specific wavelengths of light.

• nD = yellow (587.6nm or 589.2 nm)

• nF = blue (486.1 nm)

• nC = red (656.3 nm)

What is the wavelength of yellow light?

(helium/sodium)

587.6 nm or 589.2 nm

What is the wavelength of blue light?

(hydrogen)

486.1 nm

What is the wavelength of red light?

(hydrogen)

656.3 nm

How are materials classified?

By BOTH:

• Index of Refraction

• Abbe number

Abbe Number Equation:

(nD-1 / nF-nC)

Is the refracted angle negative or positive?

Positive.

Is the reflected angle negative or positive?

Negative.