Light follows a path along which the time taken is a minimum.
C stands for CELERITAS which is latin for swiftness.
What's hard to comprehend about light is that an object traveling close to the speed of light
and emitting a light beam will observe this light beam ahead still at the full speed of C.
The photon, having no charge, is its own antiparticle. Pairs of electrons and positrons can
be created spontaneously by photons, and can be made to turn into photons in the reverse process
of annihilation.
About 50 atoms can be placed end to end along a single wavelength of light.
[According to my calculations this should be more in the order of 1000 atoms. Also, it takes about
2.5 million wavelengths to traverse 1 mm of distance.]
It takes only 5 or 6 photons to activate a nerve cell via the human eye and pass a message
to the brain. If we could see 10 times more sensitively, then we would see very dim light of a particular
colour as a series of intermittent little flashes of equal intensity.
The energy of an atom is precisely related to its wavelength. An atom absorbing a photon provides
energy for an electron to move to an orbit further away from the nucleus. When an electrom falls
into the old orbit, it emits a photon with the same energy - the energy corresponding to the gap
between the orbits.
Note that the light you see 'reflected' doesn't consist of the same photons that reached the
object in the first place.
Each element is capable of generating only photons of a few specific frequencies (colours),
hence it has a unique spectrum.
When we look at photons on a large scale, the rules are approximated by Light travels in
straight lines. But when the space becomes small, such as the pinholes in the double slit experiment,
those rules fail. The same holds true for electrons; on a large scale they travel like particles
on definite paths, but on a small scale, such as inside an atom, there is no main path - and interference
reins.
Space and time are not constants. Time slows down near the speed of light. Speed of light is the true constant.
A body radiates energy not in a continuous stream, but in discrete bundles called quanta. Each
of these bundles of energy carries the amount of energy that is a multiple of its frequency. The
higher the frequency, the higher the energy. The equation for calculating the energy of a bundle
of, say, light from its frequency is called Planck's Law. The constant that accomplishes
the conversion is Planck's Constant. Einstein extended this idea for light, whose
discrete bundles could knock electrons out of a metal - calling the light quanta photons.
However the term photon is often extended to comprise any quanta of the electro-magnetic spectrum.
A wavelength of light is around 4 . 10-7 meters. 1 milimeter contains roughly 2.5
million wavelengths.
If you are a photon, traveling at the speed of light, then it's true that you sense no passage of time; everything
becomes simultaneous.
Photons carry energy in proportion to their frequency.
Photons came about, at the turn of the 19th century, as a consequence of the German physicist Max Planck's solution to a
difficult puzzle presented by classical physics: the black body radiation.
Green light will expel electrons from a piece of sodium metal, but to knock electrons out of more common metals, such as
copper or aluminium, you need to go to more energetic ultraviolet light. Moreover, it was found that, once electron
liberation has begun, turning up the intensity of the light increases the number but not the energy of the electrons that
are popped out, while turning up the frequency of the light brings out electrons of higher individual energy, but at the
same rate as before. These facts are hard to understand using a wave theory of light, in which the energy carried by waves
is a product of the frequency and the intensity.
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