PHYSICS OF LIGHT

DE LA LUNA, MARGARETTE A.

QUIROS, ELLYSA CHARISE M.

Introduction• Light is a transverse, electromagnetic wave that can be seen by

humans.• Light is sometimes also known as visible light to contrast it from

"ultraviolet light" and "infrared light".• The amplitude of a light wave is related to its intensity.

-Intensity is the absolute measure of a light wave's power density.-Brightness is the relative intensity as perceived by the

average human eye.

Introduction• The wavelength of a light wave is inversely proportional to its

frequency.

Introduction• "Is light a wave or a stream of particles?“• The fact is that light exhibits behaviors that are characteristic of

both waves and particles.• Albert Einstein discovered the nature of light as stream of

particles. • In 1678, Christiaan Huygens (1629–1695) he argued in favor

of the wave nature of light. Huygens stated that an expanding sphere of light behaves as if each point on the wave front were a new source of radiation of the same frequency and phase.

BEHAVIOR OF LIGHT• Reflection is the change in direction of a wavefront at an

interface between two different media so that the wavefront returns into the medium from which it originated.

• The law of reflection says that for specular reflection the angle at which the wave is incident on the surface equals the angle at which it is reflected. Mirrors exhibit specular reflection.

BEHAVIOR OF LIGHT• Refraction of waves involves a change in the direction of waves

as they pass from one medium to another. Refraction, or the bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves.

• If the medium (and its properties) is changed, the speed of the waves is changed.

• The most significant property of water that would affect the speed of waves traveling on its surface is the depth of the water. Water waves travel fastest when the medium is the deepest. Thus, if water waves are passing from deep water into shallow water, they will slow down.

BEHAVIOR OF LIGHT• Waves traveling from the deep end to the

shallow end can be seen to refract (i.e., bend), decrease wavelength (the wavefronts get closer together), and slow down (they take a longer time to travel the same distance). When traveling from deep water to shallow water, the waves are seen to bend in such a manner that they seem to be traveling more perpendicular to the surface. If traveling from shallow water to deep water, the waves bend in the opposite direction.

BEHAVIOR OF LIGHT• Reflection involves a change in

direction of waves when they bounce off a barrier; refraction of waves involves a change in the direction of waves as they pass from one medium to another; and diffraction involves a change in direction of waves as they pass through an opening or around a barrier in their path.

What can a light wave do when it encounters matter?

• REFLECTION-specular reflection of light by a mirror-diffuse reflection of the light in this room off all the other students-reflection is re-radiation of light by the electrons in the

reflecting material• ABSORBED

-Cyan light shining on a red apple is absorbed by electrons in the apple

A light wave shining on molecules in the air or plastic or other “transparent” materials can be

• SCATTERED-Light ray moves over to the side in all directions rather than forward, backward or being absorbed. -Intensity of the scattered light can depend on wavelength

RAYLEIGH SCATTERING

• Light waves with shorter wavelength scatter more

• Our eye sensitivity to the blue color is much stronger than that to violet.

RAYLEIGH SCATTERING Think of white light from sun as a mixture of R, G and B

Blue is scattered the most so sky looks blue when we look away from the sun

For same reason sun looks yellow (red + green)

More atmosphere allows next shortest wavelengths (green) to scatter so sunset looks red