1. Electromagnetic Spectrum
NATURE OF LIGHT
Electromagnetic Spectrum

2. Electromagnetic Spectrum
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. Electromagnetic Spectrum
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. Electromagnetic Spectrum
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. Electromagnetic Spectrum
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. Electromagnetic Spectrum
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. Electromagnetic Spectrum
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. Electromagnetic Spectrum
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. Spectroscopy
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. Spectroscopy 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. Types of Spectrum 1. Continuous Spectrum 2. Dark-line Spectrum
3. Bright-line Spectrum

12. Types of Spectrum 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. Types of Spectrum 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. Types of Spectrum 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).

15. Spectrum

16. Spectrum
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. Spectrum 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. TWO FACTORS CONCERNING A RADIATING BODY
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

19. Sodium lines

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