2.1 Introduction
2.2 Generation of Electromagnetic Waves
2.2.1 Speed of Electromagnetic Waves
2.2.2 Direction of Propagation of Electromagnetic Waves
2.2.3 Doppler Effect of Electromagnetic Waves
2.3 The Electromagnetic Spectrum
2.4.1 Energy Carried by Electromagnetic Waves
2.4.2 Radiation Pressure
2. Summary
Unit 2 - Multiple Choice - Electromagnetic Waves Questions
Unit 2 - Multiple Choice - Electromagnetic Waves Answers
Unit 2.1 Multiple Choice Extended Questions - Waves
Unit 2.1 Multiple Choice Extended Answers-Waves
 

Unit 2 Electromagnetic Waves

2.3 The Electromagnetic Spectrum

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The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation.

Gamma-Rays

— are electromagnetic radiation from the nucleus as a part of a radioactive process.

— the energy of nuclear radiation is extremely high.

— the gamma ray photon may in fact be identical to an x-ray butthe terms x-ray and gamma rays are statements about origin rather than implying different kinds of radiation.

— in interactions with matter, gamma rays are ionizing radiation and produce physiological effects which are not observed with any exposure of non-ionizing radiation, such as the risk of mutations or cancer in tissue.

X-ray

— highly penetrating rays which emanated when high energy electrons struck a metal target.

— used in medical facilities to image broken bones.

— also produced when electrons make transitions between lower atomic energy levels in heavy elements.

— in interactions with matter, x-rays are ionizing radiation and produce physiological effects which are not observed with any exposure of non-ionizing radiation, such as the risk of mutations or cancer in tissue.

Ultraviolet

— just below the visible in wavelength is called the near ultraviolet.

— tissue effects of ultraviolet include sunburn, but can have some therapeutic effects as well. The eyes are quite susceptible to damage from ultraviolet radiation.

— the sun is a strong source of ultraviolet radiation, but atmospheric absorption eliminates most of the shorter wavelengths.

Visible Light

— the narrow visible part of the electromagnetic spectrum corresponds to the wavelengths near the maximum of the Sun's radiation curve.

— in interactions with matter, visible light primarily acts to elevate electrons to higher energy levels.

— white light may be separated into its spectral colors by dispersiondue to refraction.

Infrared

— a broad range of frequencies, beginning at the top end of those frequencies used for communication and extending up the the low frequency (red) end of the visible spectrum. The wavelength range is from about 1 millimeter down to 750 nm.

— adjacent to the visible spectrum is called the "near infrared" and the longer wavelength part is called "far infrared".

— in interactions with matter, infrared primarily acts to set molecules into vibration.

— does not penetrate the atmosphere well.

Microwaves

— are good for transmitting information from one place to another because microwave energy can penetrate haze, light rain and snow, clouds, and smoke.

— shorter microwaves are used in remote sensing. These microwaves are used for radar like the doppler radar used in weather forecasts.

— cause water and fat molecules to vibrate, which makes the substances hot.

Radio waves

— are also given off by stars, sparks and lightning, which is why you hear interference on your radio in a thunderstorm.

— Radio waves are the lowest frequencies in the electromagnetic spectrum, and are used mainly forcommunications.

Radio waves are divided into:

— Long Wave - around 1~2 km in wavelength.

— Medium Wave - around 100m in wavelength, used by "AM" stations.

— VHF

— wavelengths of around 2m.

— "FM" radio stations, such as BBC Radio 1and Further up the VHF band are civilian aircraft and taxis.

— UHF

— wavelengths of less than a metre.

— used for Police radio communications, television transmissions and military aircraft radios.

Energy increases with increasing frequency

 

   

 

 

     
Concept by Kishore Lal. Programmed by Kishore Lal... Copyright © 2015 Kishore Lal. All rights reserved.