• Are waves that do not require a material medium for their transmission.
  • They are formed by magnetic and electric disturbances which are at right angle to each other.
  • They are arranged in either order of increasing wavelength or decreasing frequency. This forms a spectrum called electromagnetic spectrum.
  • Examples of electromagnetic waves include;
  1. Gamma rays.
  2. X- Rays.
  3. Ultra violet rays.
  4. Visible light.
  5. Infra-red.
  6. Micro wave.
  7. Radio wave.

                        Properties of electromagnetic waves.

  1. They travel in a straight line with the speed of light, 3 X 108, that is, they all travel with the same velocity.
  2. They do not require a material medium for their transmission.
  3. They possess energy in different amounts depending on frequency.
  4. They do not carry charges hence are not affected by electric and magnetic fields.
  5. They are progressive transverse waves in nature.
  6. They undergo reflection, refraction, diffraction, interface and polarization effect.
  7. They cause photoelectric effect.

Gamma rays.

  • They are at the extreme end of the spectrum with the highest frequency (X 1023 Hz) and shortest wavelength (X 10-14).
  • They have the highest energy.


  • They are produced by radioactive substances during beta decay.
  • They are produced by energy changes in the nucleus of a radioactive atom.


  • They can be detected by using photographic plate or film or by using radioactive detectors e.g. Geiger- Muller tube. (GM tube).


  1. To sterilize food and medical instruments.
  2. To kill weevils.
  3. To treat cancer.
  4. To measure the thickness of a material e.g. a paper.
  5. To detect the flow of very tiny holes.


  1. X- rays.
  • They are next to gamma rays. They have high frequency and short wavelength.


  • They are produced in X- rays tube by bombardment of a target metal atom by fast moving electrons.
  • They are produced by energy transition in an atom.


  • By using photographic plate or film or fluorescent barium plantincyte material.
  • By use of gas discharge tube.

                                    Uses of X- rays.

  1. In radiography and radiotherapy.
  2. Treatment of cancer.


Ultra violet rays.

  • Are next to X- rays and beyond visible violet light.


  • Produced by the sun or mercury vapor lamp.
  • Produced by electric sparks.


  • Can be detected by using photographic film, fluorescent materials e.g. quinine sulphate, paper smeared with Vaseline, using skin as they cause sunburn and tanning, using photo cells.

                                    Uses of ultra violet rays.

  1. Detect forgeries.
  2. Make fluorescent materials mixed with washing powder or detergent to fluorescence or flow or shine.
  3. Make clothes washed with detergents to be brighter.
  4. In food technology, radiation is used to detect freshness of an egg. A fresh egg glows with reddish color whie the other with violet color.
  5. Used in medicine to kill bacteria, that is, in skin treatment.
  6. Source of vitamin D.
  7. Used in road signs. It makes the paint in road signs and vehicle reflectors to glow.


  1. Visible light.
  • It is next to ultra violet and has long wavelength (X 10-7) and consists of seven colors that is red, yellow, orange, blue, green, indigo and lastly violet.


  • By use of eyes, photographic films and photo cells.

                                    Uses of visible light.

  1. For visibility.
  2. Light is converted to other forms of energy e.g. electric energy.
  3. Light is used in photosynthesis.
  4. Light is used in drying of clothes and harvested crops.
  5. Used in photography.
  6. Used in optic fibers.


  • It is next to visible light. It is beyond visible red with low frequency and long wavelength.


  • Produced by the sun or any red- hot object.
  • They are produced as a result of small energy changes of an electron in an atom or molecule vibration.


  • They can be detected by using a thermometer with a blackened bulb, thermopile, bolometer and by the use of skin. Heating effect produced by the skin.

                                    Uses of infrared.

  1. In agriculture used in greenhouse.
  2. In photography used in cameras that use infrared.
  3. Used in wars as missiles follow the jet which emits IR.
  4. Used in cooking, heating or warming a room.
  5. Used in drying grains or fish.

Micro waves.

  • Have high frequency than radio waves and are next to infrared.


  • They are produced by special vacuum tube called magnetrons in microwaves, ovens or maser.


  • They are detected by use of crystal detector or solid state diodes.

                                    Uses of micro waves.

  1. As a source of heat in ovens. Waves are reflected from a metal stimer to different parts of the oven. The wire mesh on the door also reflect micro wave back to the food. Precaution in using a microwave is to always switch off the device before opening the door.
  2. In communication. Micro waves are sent into space by the radar. These waves are reflected back to the radar system on hitting an object in space. The time taken for the pulse to travel and to end from is recorded. This time interval is used to determine;
  3. Position of an object is space.
  4. The speed of the object e.g. aircraft. To determine the speed of an object, the differences in the frequency between the sent signal and reflected signal is used.
  • To indicate the presence of an object in space.
  1. It is used in polices peed check.
  2. Radar technique is used;
  3. To measure the distance between earth and a planet.
  4. To map the distance between earth and a planet.
  • To map the solar system.


  • Radio waves.
  • Radio waves are in the extreme end of the spectrum with low frequency and long wavelength.


  • Produced by oscillating electrical circuit called oscillatory circuits and are transmitted through antennae or aerial.


  • They are detected by using resonant circuit in radio and TV receivers.

                                    Uses of radio waves- radio frequency band.

Frequency band


Low frequency

300 KHz

Long waves radio and communication over large distance


Medium frequency

300 KHz – 3MHz

Medium wave. Local and distance radio reflected by ionosphere hence long range.


High frequency

3 – 30 MHz


For short wave radio and communication amateur.


Very high frequency

30 – 300 MHz


FM radio and police radio and meteorology devices.


Ultra high frequency

300 – 3000 MHz


TV (bands 4 and 5). Aircraft landing system.






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