Tutorial - Light as Particle vs Wave    Std 1j

Particle-like behavior

When the book refers to particles they are referring to photons.  Photons are not really particles, but the following things they do, are actions similar to particles:

1.      a specific photon has a specific, fixed amount of energy it carries

2.      you can only change a photon’s energy by changing its wavelength or absorbing it in an atom.

3.      when an atom absorbs a photon, it causes the electron to “jump” to a specific new energy level above the nucleus (quantum leap).

All three of these occur for visible light and all other electromagnetic radiation.

Actually, photons are not particles in the physical sense that we normally associate with that word. Rather, they consist of discrete bundles of energy which are fixed in magnitude. As a result, each photon takes on some of the characteristics of a physical particle.  If you want to know more go to:

Wave-like behavior

Physical waves such as those traveling over the surface of water, tend to go around barriers when they hit them.  See video at 2-slit experiment – animated video explaining wave vs particle behavior of electrons (YouTube) – very clear & simple particle vs wave explanation!!!

When waves go through slits (as show in the video above), they tend to interfere with each other.  The famous 2-slit experiment using litght, tends to do the same thing.  You can see an animation of this at 2-slit experiment – wave interference, fuzzy edges – great applet (Physics 2000) .  For a good video of wave interference go to Wave interference – water & electronic - great applets (Physics 2000) .  Wave interference causes the edge of an object to have a fuzzy line when a laser is shown on it and projected towards a flat surface.  This suggests that light travels in waves.

Photons travel at different speeds in different media.  For instance, in a vacuum (no medium) photons travel at the speed of light.  In water they slow down, however they continue at this new slow speed as far as they travel in the medium.  A particle would continue to slow down the further it went in the medium.  Different media could be the atmosphere, water, oil or any other optical material such as glass, diamons etc.  The animation below is very interesting.

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