Further Exploration of Light Patterns

Spectra of Gases

When one atom produces light, it emits one photon.  Thus, in our investigations we will be primarily interested in the energy of individual photons. As we will see, this energy will tell us something about the atoms of a material. Thus, the color of a light will be an important variable.  Each photon of visible light carries a very small amount of energy.  This energy ranges from about 2.56 x 10^-19 Joules for red light to 4.97 x 10^-19 Joules for violet.  Using these very small numbers is inconve­nient, so we will use different units – the electron volt (eV).  In these units, visible light energies range from about 1.6 eV (red) to 3.1 eV (violet) – much easier num­bers to deal with.  the figure below so the relation between color and the energies of photons in electron volts.   For a little more on the electron volt follow this link.

The colors of the visible spectrum with the energies of the photons for the various colors. 

Note that this figure was created in Europe where they use commas instead of period for decimal points.

That is 1,65 in Europe = 1.65 in the US

(Wikimeida Commons, public domain)

The brightness of the light is related to the number of photons emitted.  A dim light will emit fewer photons than a bright light. Thus, we have two measures of energy
— brightness and color.  Because color is related to the energy of the light (photons) from each individual atom, we will concentrate on it. 

Most light is composed of several different colors.  To separate the colors we use a spectroscope similar to the one that you built in the previous activity.

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