Electromagnetic Waves

Are waves produced by electromagnetic vibrations.

ELECTR OMAGNETIC SPECTTRUM

Is a band of all electromagnetic waves arranged on order of increasing or decreasing frequency or wavelength change.

PROPERTIES OF ELECTROMAGNETIC WAVES

Electromagnetic waves are transverse waves which exhibit the following characteristics.

         i.            They do not require a material medium to travel through.

       ii.            They undergo reflection, refraction, interference and diffraction.

     iii.            Travel at the speed of light.

     iv.            They carry no electric charge

       v.            They transfer energy from a source to a receiver in the form of oscillating electric and magnetic fields.

     vi.            They obey the wave equation C =¦λ

RADIO WAVES

Are waves with the longest wavelength in the electromagnetic spectrum.

Radio waves are categorized into:

         i.            Long waves (LW)

       ii.            Medium waves(MW)

     iii.            Short waves(SW)

TYPES OF SHORT WAVES

         i.            VERY HIGH FREQUENCY (VHF)

       ii.            ULTRA HIGH FREQUENCY (UHF)

DECTION OF RADIO WAVES

Are detected using specially designed antennae such as those used in radios and televisions.

USES OF RADIO WAVES

         i.            Broadcasting of information by radio and television channels is achieved using radio waves.

       ii.            Astronomers use large radio telescopes to collect and study radio waves from distant stars and galaxies.

SOURCES OF RADIO WAVES

         i.            Alternating electric currents (A.C) flowing in special conductors called antennae.

       ii.            Special circuits called oscillators

     iii.            Objects in space such as planets, comets, stars and galaxies.

MICRO WAVES

Are waves with a short wavelength of between 10^-4 m to about 0.1 m.

SOURCES OF MICROWAVES

         i.            Are produced by oscillation of charges in special antennae mounted on dishes

       ii.            Are also produced in devices called magnetrons.

DETECTION OF MICROWAVES

Microwaves can be detected using special receivers which convert radio wave energy to sound.

RADAR, which is an acronym for ²Radio detection and ranging” is a technology which uses radio waves to detect and determine the position of objects.

USES OF MICROWAVES

         i.            Used in cooking e.g. in microwave oven, microwaves pass the food and absorbed by the food molecules. The absorbed energy causes the molecules to rapidly vibrate producing heat that heats or cooks the food.

       ii.            Radar system use micro waves to detect the position, speed, and other characteristics of remote objects.

     iii.            Are used in long-distance Communication, because they are not affected by clouds or other atmospheric conditions.

INFRA – RED WAVES

Are electromagnetic waves that have a frequency of between 10¹² Hz and 10¹⁴ Hz. They lie between visible light and microwaves.

SOURCES OF INFRA-RED WAVES

         i.            Are produced by the vibration of atoms and molecules due to their thermal energy.

       ii.            All hot bodies emit infrared radiations.

DETECTION OF INFRA-RED

Infra-red radiation is invisible to the human eye.

The devices used to detect infrared radiation include black bulb thermometers, photographic films, thermometers and photo transistors.

USES OF INFRA-RED WAVES

         i.            Are used to cook food in conventional ovens.

       ii.            Infrared with wavelengths near the visible light are used in remote controller telecommunication and security system.

     iii.            Infrared radiations are used in infrared photography.

VISIBLE LIGHT

Is the narrow range of electromagnetic wave frequencies to which human eyes are sensitive.

SOURCES OF VISIBLE LIGHT

Are produced by electron transitions with an atom

Approximately 50% of the radiations emitted by the sun are visible light. We see objects because they either emit visible light or they reflect visible light from other sources.

DETECTION OF VISIBLE LIGHT

They are detected by the eyes, photographic films and photocells.

USES OF VISIBLE LIGHT

         i.            They are used in vision

       ii.            They are used in photography

     iii.            They are used in photosynthesis by plants.

     iv.            They are used to produce electrical energy by photo cells.

ULTRA – VIOLET

Are electromagnetic waves with shorter wavelength than visible light.

SOURCES OF ULTRA – VIOLET

         i.            Produced by electron transitions in atom like those that produce visible light but more energetic.

       ii.            Are also emitted by very hot objects.

     iii.            The sun emits ultra violet radiation.

     iv.            Electric arcs used for welding also emit Ultra-violet radiation.

NOTE

Most of the ultra-violet radiation is absorbed by the atmosphere’s ozone layer.

DETECTION OF ULTRA-VIOLET

         i.            Detected by photographic films

       ii.            Fluorescent materials which absorb ultra – violet light and re-emit it as visible light.

USES OF ULTRA VIOLET

         i.            Simulates the production of vitamin D in the human skin

       ii.            Used in the treatment of the skin conditions such as psoriasis

     iii.            Used as a germicidal agent in the sterilization of food and the purification of air and water.

     iv.            Fluorescent materials absorb ultra- violet radiation and re-emit it as visible light.

       v.            Used in banks to detect forged documents and fake currencies

     vi.            Used in extensively in astronomical observations.

WARNING

A prolonged exposure to solar ultra-violet can lead to damages on the skin, eyes and the immune system.

X – RAYS

Are electromagnetic waves with short wave lengths and very light frequency X- rays also are known as ionizing radiation.

SOURCES OF X – RAYS

X – Rays are produced when electrons that have been accelerated to very high velocities hit a metal target. This process takes place in an x- ray tube.

DETECTION OF X – RAYS

         i.            Using a photographic plate.

       ii.            Using an x – ray film in a cassette.

     iii.            Using rare – earth element screens

USES OF X- RAYS

         i.            Used in x – ray photography

       ii.            Are used in the diagnosis and treatment of cancer.

  

GAMMA RAYS

Are the most energetic of the electromagnetic waves.

SOURCES OF GAMMA RAYS

         i.            Are produced in space by things such as solar flares, supernovae, neutron stars, black holes and active galaxies.

       ii.            Are also produced by radioactive decay of atoms (natural radioactivity).or nuclear fission (in atomic bombs and nuclear reactors).

DETECTION OF GAMMA RAYS

Gamma rays are detected by using;

         i.            Photographic films

       ii.            Geiger – Muller tube

     iii.            Cloud chamber

USES OF GAMMA RAYS

         i.            Used in agriculture to obtain new plant varieties which are disease – resistant and give more yields.

       ii.            Are also used in the diagnosis and treatment of cancer.