Light
LightLight is what we see. It can be thought of either as a particle, (the photon), or as a wave. The photon we can easily think of as a small dot travelling through space at the speed of light. Each photon has a particular colour or energy. But how do we think of light as a wave? For this we need to know that light is also an "Electro-magnetic field" -- a combination of electric-field and magnetic-field -- the same thing that causes static electricity and magnets to attract (or repel) things. Light is just another way that this "field" is experienced. A light wave is an oscillating electro-magnetic field - just like a water wave is water with an oscillating surface. Photons are bosons, and have a quantum spin of 1.
Light has the properties of both particle and waves. If we look for photons we will find them, but if we look for wave -like properties we can see them too. However, we cannot see both particle and wave properties at the same time.
It is often useful to confine light in an optical-cavity. This allows us both to make more intense light, as well as select light of a particular colour (or energy).
� Light travels at a speed of 2.99792458x10^{8} ms^{-1}
� When passing though matter, light is slowed down by brief interactions, and so appears to travel more slowly.
� This "slowing down" is accounted for by the index of refraction of the matter.
Light's properties can at first seem confusing and inconsistent because of
the unique nature of light: light has the properties of both a wave and a
particle. In some situations, light's behavior is more easily explained by
thinking of light as a particle. In other situations, its behavior can only be
explained if light is thought of as a wave. This duality of light between a
particle and a wave is very difficult if not impossible to visualize. Instead
it is much easier to see light demonstrate its properties in specific
situations.
Light as a Wave
Before the nineteenth century, the physics community was split over the
actual nature of light. Around 1800, Thomas Young devised an experiment
designed specifically to settle the debate over the nature of light once and
for all. The basic principle behind the experiment was how light would
behave when it encountered an obstacle with a hole that was smaller than
the beam of light. Young set up a beam of light to shine through a slit,
then the resulting light that made it through that...
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