Properties of Light

Radiation

• Information from the Cosmos

Radiation,Waves, & Information

• Most of the information around us gets to us in waves.
• Sound energy that travels to our ears is in one form of wave.

• Light is energy that comes to our eyes if the form of another type of wave.
• Energy (information) that is transferred from place to place in the form of a wave is called RADIATION.

Information from the Cosmos

• Until recently, our knowledge of the universe was obtained only by studying the visible light that happened to arrive on Earth.
• Since the 1930’s, possible to study other types of radiation and particles ---
• radio waves, X-rays, gamma rays, cosmic rays, neutrinos, and gravitational radiation.
• To understand the methods used to study the cosmos, we must understand the basic nature and behavior of light.

So, what is light?

• The particle or ray model of light is illustrated by the properties of reflection and refraction.

• But there are problems: if light is a wave, and waves need a “medium” such as air or water to carry them, then how can light travel through empty space?

• The solution was to decide that light was neither a wave nor a particle, but something else which sometimes behaved like them.

• Is it a wave?

• Is it a particle?

• It is neither, but it’s like both

• The wave model of light is illustrated by the properties of reflection, refraction, diffraction, interference, and polarization.

What is a Wave?

• Wave motion is NOT a mechanical phenomenon because a wave is not a material object but a form.
• It cannot be assigned a mass, and the concept of acceleration cannot be applied to a wave.
• The motion of a wave is vastly different from the motion of the medium in which it travels. In fact, a wave can exist without any movement of matter at all!
• So, what is a wave? It is a pattern or form that moves.
• It can be a
• deformation of a material object (music string or waves on the surface of a body of water)
• OR
• pattern in a field (light or radio waves).