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Chapter 4: Light and Atoms

Terms in this set (40)

•Hot objects emit light (ex: stove burner).
•The hotter the object gets, the brighter the light and the changing of colors (orange, to red, to yellow, to blue).
•As an objects temperature increases, the object radiates light more strongly at shorter wavelengths.
•This allows astronomers to measure the temperature of stars from their light.
•We can find a numerical value for the temperature using a relation first worked out by Wienn*.
Wien's Laww* states that the wavelength (color) at which an object radiates most strongly is inversely proportional to the objects temperature (hottest:485 nm, coolest:725 nm, intermediate:580 nm).
•You might note that the wavelength at which the Sun radiates most strongly corresponds to a blue green color, yet the Sun looks yellow white to us. The reason we see it as whitish is related to how our eyes perceive color.
-physiologists have found that the human eye interprets sunlight (and light from all extremely hot bodies) as whitish, with only tints of color.
•Sunspots are stormy regions on the surface of the Sun that are cooler than surrounding regions. Sunspots are actually very bright, but because their temperature is typically about 4500K, they look dark and somewhat reddish in color in contrast to the 6000K surrounding regions.
•Although Wien's Law works accurately for most stars and planets, it has some important exceptions. For example, the red color of an apple and the green color of a lime come from the light they reflect and have nothing to do with their temperature.
•Wien's Law is exact only for a class of objects known as blackbodies. A blackbodyy* is an object that absorbs all the radiation falling upon it. Because such a body reflects no light, it looks black to us when it is cold.
•When an electron moves from one orbital to another, the energy of the atom changes.
-if the atoms energy is increased, the electron moves outward from an inner orbital. Such an atom is said to be excited.
•Although the energy of an atom may change, the energy cannot just disappear.
•One of the fundamental laws of nature is the Conservation of Energyy*. This law states that energy can never be created or destroyed, it can only be changed in form.
-according to this principle, if an atom loses energy, that energy must reappear in some other form. One important form in which the energy reappears is light, or, more generally, electromagnetic radiation.
•How is the electromagnetic radiation created? When the electron drops from one orbital to another, it alters the electric energy of the atom. Such an electrical disturbance generates a magnetic disturbance, which in turn generates a new electrical disturbance.
•Thus, the energy released when an electron drops from a higher to a lower orbital becomes an electromagnetic wave, a process called emissionn* (ex: aurora borealis/northern lights).
•The reverse process, in which light is stored in an atom as energy, is called absorptionn*. Absorption lifts an electron from a lower to a higher orbital and excites the atom by increasing the electrons energy.
•Emission and absorption are particularly easy to understand if we use the photon model of light; according to this model, an atom emits a photon when one of its electrons drops form an upper to lower orbital. Similarly, an atom absorbs light when a photon of the right energy collides with it and knocks one of its electrons into an upper level.