Electromagnetic Spectrum

NATURE OF LIGHT

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.

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.

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.

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)

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.

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.

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.

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.

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.

Types of Spectrum

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

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

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.

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).

Spectrum

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.

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.

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

Sodium lines

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