|www.nortonkit.com||18 अक्तूबर 2013|
|Digital | Logic Families | Digital Experiments | Analog | Analog Experiments | DC Theory | AC Theory | Optics | Computers | Semiconductors | Test HTML|
|Direct Links to Other Optics Pages:|
|Basic Concepts:||[What Is Light?] [Light as a Wave] [Light as a Particle] [The Characteristics of a Photon] [The Photoelectric Effect] [The Transverse Electromagnetic Wave (TEM)]|
|Reflection and Refraction:||[Introduction] [Reflection, Part 1] [Reflection, Part 2] [Refraction, Part 1] [Refraction, Part 2]|
|Lenses:||[Introduction] [The Convex Lens]|
|Fiber Optics:||[Introduction] [Fiber Optics, Part 2] [Fiber Optics, Part 3] [Fiber Optics, Part 4] [Fiber Optics, Part 5] [Fiber Optics, Part 6]|
|Light as a Particle|
While it remains true that light exhibits the properties of an electromagnetic wave as described on the page on Light as a Wave, there are other characteristics of light, discovered more recently, which imply that light also partakes of some of the properties of a physical manifestation. In this context, light behaves in some ways as if it consists of discrete particles rather than infinitely variable waves. These apparent particles have been designated photons.
Some of these characteristics are:
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.
Viewed in this context, light still does not change its basic behavior. These apparent particles are electrically neutral, so they tend to travel in straight lines, without being affected by either magnetic fields or electrical fields.
If photons were actual physical particles, we would have trouble using them to explain some of the observed behaviors of light. For example, when light passes from a vacuum to a denser medium, such as Earth's atmosphere, it slows down in accordance with the density of the medium. This much, at least, makes intuitive sense. However, light then maintains a constant speed through the new medium it does not continue to slow down as it continues to move. This does not seem to make much sense for physical particles, which should be subject to friction effects in a non-vacuum. Furthermore, when the light leaves the denser medium for a less dense one, it speeds up again. Definitely not the behavior one would expect from any kind of particle.
But if we examine a photon as a bundle of energy that simply exhibits some of the characteristics of a physical particle, things begin to make more sense. We know by experiment that a photon can transfer its energy to an electron. The photoelectric effect occurs when photons of sufficient energy actually kick electrons off of the surface being struck by light. But even if a given electron hasn't received enough energy from a photon to free it from its material surface, it can receive enough energy to raise it to a higher orbit around its parent nucleus, or even free it from that nucleus. In such cases, the electron can hold that energy for a period of time before falling back to its usual lower-energy orbit and releasing the energy again. This effect explains many phenomena that we can observe directly.
When the photon impacts with the electron, it imparts its energy to the electron. There are several possible results, depending on the energy in the photon:
So what is a photon, in a scientific sense? Let's take a look at that on the next page: Characteristics of a Photon.
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