Refraction and Lenses

Refraction• The change in direction or ‘bending’ of light.

Snell’s Law• Snell came up with a way to figure out how far light will ‘bend’

depending upon the medium the light traveled from and to.

Link to interactive Snell’s Law AppletWillebrord van Roijen Snell

1580-1626

Snell’s Actual Law

n1 is the index of refraction for the incident medium.

n2 is the index of refraction for the refracting medium.

θ1 is the incident angle

θ2 is the angle of refraction

Link to Überdork’s ridiculous tribute to Snell’s law.

Example Problem 1• A light beam in air hits a smooth lake at an angle of 30

degrees. At what angle is it refracted?

Index of Refraction and the Speed of Light

n = index of refraction

c = 3x108 m/s

Vmaterial = Velocity of light in that material

mediumV

cn

Total Internal Reflection• Total internal reflection is a phenomenon that happens only

when light passes from a more optically dense medium to a less dense optical medium. The incident ray’s angle is so ‘great’ that there is no refracted ray.

Link to Total Internal Reflection Animation

Applications of Total Internal Reflection

• Mirages

• Fiber Optics

• Diamonds

Turn yourself into a diamond

Example Problem 5• Find the critical angle for diamond.

Example Problem 6• The critical angle for a special glass in air is 41 deg.

What is the critical angle if the glass is immersed in water?

Dispersion of Light• The separation of light into it’s spectrum is called dispersion.

http://www.pbase.com/agroni/night_photography

Lenses• Lens: Any transparent material with an index of refraction

greater than that of air which re-directs lights path

Lens Equations

Convex Lens Anatomy

Convex Example Problem

Concave Lens Anatomy

Chromatic AberrationChromatic Aberration – A defect where different colors are focused at different spots, especially at edges. Objects appear to be ringed in color.

Lens Applications

Nearsighted / Farsighted

Cameras