Light is also called radiation, and it all travels at the speed of light, c, which is 300,000 km per second!
Light is a form of energy!
Light has the properties of both a particle and a wave. Light particles are called "photons". The amount of energy a photon has depends on it's wavelength (ah, a wave property!).
In addition to visible light, there are various forms of "light" we cannot see. Listed below are the various types of radiation, from the highest energy photons to the lowest energy photons.
Visible light has wavelengths between 4000 A (violet light) and 7000 A (red light). Note that since violet light has a shorter wavelength than the red light, the violet photon has more energy than the red photon.
Temperature is a measure how much heat energy an object (such as an atom or molecule) has. The heat energy is related to how fast these atoms or molecules are moving or vibrating. The hotter an object gets, the faster the atoms or molecules will be moving or ibrating.
A molecules in a solid can be pictured as a bunch small balls in a crystal pattern attached to the neighboring molecules by springs. When heat is added, the molecules vibrate pulling on these springs. The hotter they get, the more they will stretch and pull on these springs. When enough heat is added, they can break the springs and when this happens, a solid becomes a liquid.
In a liquid, the molecules are free to move around randomly, but they are still close to other molecules and bounce off of them. By adding more heat energy, these collisions become very hard. When enough heat is added, the collisions be hard enough that some of the molecules free themselves from the liquid. These molecules are now in a gaseous state.
As heat is added to an object, the molecules
move faster. So, as heat is removed the
molecules will move slower.
Image continually removing heat from an object. The molecules will continue to move slower and slower. At some point, a temperature will be reached at which the molecules will stop moving. This temperature is the lowest temperature possible and is know as ABSOLUTE ZERO! This turns out to be -273° C.
This is an excellent starting point for a
temperature scale and is the starting point for
the Kelvin temperature scale.
Celsius (or Centigrade) temperatures can be converted to Kelvin temperatures simply by adding 273 to the Celsius temperature.
As Absolute Zero is the starting point for the Kelvin scale, there are no negative temperatures in the Kelvin scale.
|Scale||Water Freezes||Water Boils|
|Absolute Zero||0 K|
|Room Temperature||295 K|
|Surface of Venus||750 K|
|Surface of the Sun||5700 K|
|Solar Corona||2,000,000 K|
|Core of the Sun||15,000,000 K|
|Core of a Dying Star||200,000,000 K|
|Universe 1/100 Second Young||100,000,000,000 K|
Wien's Law can also be written as
While temperature must be measured in Kelvin, the peak wavelength can be measured in various length units, which then determines the valve of the constant to be used.
If the peak wavelength is measured in nanometers, the constant has value of 3,000,000 nm K (For complete accuracy, the value is 2,900,000 nm K). If the peak wavelength is measured in microns, then the value of the constant is 3,000 micron K.
So, for any object emitting a continuous spectrum, we can determine its temperature just by measuring the wavelength of peak emission (what color is most of the light).
In the form of a heated gas, each element produces a very SPECIFIC and UNIQUE emission line pattern, much like a fingerprint of the element. This unique pattern allows the different gases in a mixture to be identified.
This is NOT TRUE for the sources of a continuous spectrum.
The hydrogen absorption line spectrum.
Note the same colors are emitted and absorbed!
The Mystery of Emission-Line Spectra
Atomic Absorption and Emission Spectra
Examples of Emission-Line Spectra
Note: The emitted energy goes as T (temperature) to the 4th power! So if I make T (the temperature) 4 times larger, the energy emitted from each square meter increases by 4 x 4 x 4 x 4 = 256 times!
How can we make an object emit more energy?
The Nearest Star: The Sun.
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