Christiaan Huygen (1629 - 1695) - Dutch mathematician, astronomer, and physicist
Refraction – the bending of a wave front as the wave front passes between two substances in which the speed of the wave differs or the bending of a wave disturbance as it passes at an angle from one medium into another
Some examples of refraction
Java Applet for Refraction
Why does refraction happen?
Law of Refraction
Index of Refraction – the ratio of the speed of light in a vacuum to the speed of light in a given transparent medium.
Indices of Refraction for Various Substances
Solids at 20˚C
Liquids at 20˚C
|Ice (at 0˚C)||
Gases at 0˚C, 1 atm
Applications of Refraction
A light beam in air hits a sheet of crown glass at an angle of 30.0˚. At what angle is the light beam refracted?
A laser beam in air is incident upon ethanol at an angle of incidence of 37.0˚. What is the angle of refraction?
A block of unknown material is submerged in water. Light in the water is incident on the block at an angle of incidence of 31˚. The angle of refraction of the light in the block is 27˚. What is the index of refraction of the material of the block?
Lens – a transparent object that refracts light rays, causing them to converge or diverge to create an image
Ray Diagrams for Lenses
Thin Lens Equation
An object is placed 32.0 cm from a convex lens that has a focal length of 8.0 cm.
a. Where is the image?
b. If the object is 3.0 cm high, how tall is the image?
c. What is the orientation of the image?
Corrective Lenses for Nearsightedness
Corrective Lenses for Farsightedness
Combination of Thin Lenses
Two converging lenses are placed 20.0 cm apart, as shown in the figure. If the first lens has a focal length of 10.0 cm and the second has a focal length of 20.0 cm, locate the final image formed of an object 30.0 cm in front of the first lens. Find the magnification of the system.
Total Internal Reflection
Total Internal Reflection–the complete reflection
of light at the boundary of two transparent media; this effect occurs when
the angle of incidence exceeds the critical angle.
Critical Angle–the minimum angle of incidence for which total internal reflection occurs
Calculating a Critical Angle
What is the critical angle for light emerging from carbon disulide into air?
One method of determining the refractive index of a transparent solid is to measure the critical angle when the solid is in air. If the critical angle is found to be 40.5˚, what is the index of refraction of the solid?
Application of Internal Reflection
Dispersion–the process of separating polychromatic light into its component wavelength
Chromatic Aberration–the focusing of different colors of light at different distances behind a lens