1. NATURE OF LIGHT

2.  The electromagnetic spectrum comprise of the following:  1. Radio waves  Electromagnetic radiation with wavelengths that range from hundreds of meters to less than a centimeter.  Familiar due to their use in communications.  AM Radio band – 540 to 1, 650 kHz.  FM band – 88 – 108 MHz  Also includes shortwave radio transmissions and television signals.

3.  2. Microwaves  Electromagnetic that range from approximately 1 ft (30 cm) in length to the thickness of a paper.  Microwave oven heat food by causing water molecule to rotate at a frequency of 2.45 GHz.  In astronomy radiation of a wavelength of 8.2 inch (21 cm) has been used to map neutral hydrogen (H) throughout the galaxy.  RADAR is also included in this region.

4.  3. Infrared  Electromagnetic radiation that comprises the region of the electromagnetic spectrum where the wavelength of light is measured from 1 mm to 400 nanometer.  Discernible to humans as heat.  Discovered by W. Herschel by dispersing sunlight through a prism and measuring the temperature increase just beyond the red end of the spectrum.

5.  4. Visible light  Electromagnetic radiation in the range visible to the human eye between approximately 4, 000 and 7, 700 angstroms.  Wavelengths to which the human eye is sensitive.  Easily pass Earth’s atmosphere.  Further broken down into the familiar color of a rainbow. (MR. ROY G. BIV)

6.  5. Ultraviolet  Electromagnetic radiation ranging in wavelength from 400 to 10 billionth of a meter.  Has many important effects on Earth.  The ozone absorbs much of the UV radiation from the sun.  UV that reaches the Earth’s surface can cause suntans and sunburns.

7.  6. X-rays  Electromagnetic radiation that are highly energetic with wavelengths ranging from about 10 billionths of a meter to 10 trillionths of a meter.  Useful in medical and industrial radiography.  Can pass through the body.  Allows doctors to study bones and teeth.  Do not pass Earth’s atmosphere so astronomers must place X-ray telescopes in space.

8.  7. Gamma rays  Electromagnetic radiation that are most energetic and are comprised of light with wavelengths of less than about ten trillionths of a meter and include waves with wavelengths smaller than the radius of an atomic nucleus (1015m).  Produced by nuclear processes during radioactive decay or in nuclear reactions in space.

9.  The study of the spectra especially to determine the chemical composition of substances and the physical properties of molecules, ions and atoms.  Study of the properties of light that depend on wavelength.  Newton’s use of prism dispersing the visible light into the rainbow of colors initiated the study of spectroscopy.

10.  Spectroscope  The instrument for studying spectra; an instrument for dispersing light, usually light in the visible range, into a spectrum in order to measure it.

11.  1. Continuous Spectrum  2. Dark-line Spectrum  3. Bright-line Spectrum

12.  1. Continuous spectrum  Is produced by an incandescent solid, liquid or gas under high pressure.  Consists of an unfiltered band of color.  E.g. Common light bulb

13.  2. Dark-line spectrum (Absorption spectrum)  Is produced when “white” light is passed through the a comparatively cool gas under low pressure.  Gas absorbs selected wavelengths of light, so the spectrum that is produced appears as a continuous spectrum but with a series of darklines.

14.  3. Bright-line spectrum (emission spectrum)  Is produced by a hot (incandescent) gas under low pressure.  It is a series of bright lines of particular wavelengths depending on the gas that produces them.  These bright lines appear in the exact location as the dark lines that are produced by this gas in a dark-line spectrum (absorption).

16.  The spectrum coming from the sun contains thousands of dark lines.  Over 60 elements have been identified by matching those lines with those elements known on Earth.

17.  TWO FACTORS CONCERNING A RADIATING BODY IS IMPORTANT  1. If the temperature of a radiating surface is directly proportional to the fourth power of its absolute temperature.  Stefan Boltzman Law  The energy radiated by a body is directly proportional to the fourth power of its absolute temperature.  Eg. Star – 2 times brighter – energy emitted will be 2 raise 4, it means the star released 16 times more energy.

18.  2. As the temperature of an object increases, a larger proportion of its energy is radiated at shorter wavelengths.  E.g.  Heated metal rod  Hot - Red color – longer wavelength  Hotter – Blue color – shorter wavelength  Red stars – hot  Blue stars - hotter