Electromagnetic Spectrum

                               Electromagnetic Spectrum 

1) Radiowaves - 

Range - 5 x 10^5 Hz to 10^9 Hz

Produced by - oscillating electric circuits having an inductor and capacitor 

Properties- 

1) Travel with speed of 3x10^8 m/s

2) Obey laws of reflection and refraction 

3) Get diffracted from obstacles coming in their path 

Applications /Uses- 

1) wireless communication purposes, transmit radio and TV signals

2) Used in radio astronomy 

2) Microwaves- 

Range- 1GHz to 300 GHz 

Produced by- special vaccum tubes, namely klystrons,magnetrons, Gunn diodes etc

Property- Produce heat, when absorbed by matter 

Uses- 

1) In radar systems.

2) In long distance telephone communication system 

3) Used for cooking 

4) In study of atomic and molecular structure 

5) Used for observing the movement of trains on rails while sitting in microwave operated control rooms.

3) Infrared ( sometimes called heat waves) 

Range- 3x 10^11 Hz to 4 x 10^14 Hz 

Discovered by - Herschell 

Produced by - hot bodies and molecules 

Few sources- Nernst lamp, Globar, LASER, 

Detect - Human eye can’t detect it but snakes do. Thermocouples, thermopiles, bolometers, photo-conducting cells are used for detection. 

Properties- 

1) Obey laws of reflection and refraction.

2) Can produce interference and can be polarised

3) it affect photograhic plate

4) When allowed to fall on matter it produce an increase in temperature

5) When observed by molecules the energy of infrared rays gets converted into molecular vibrations

6) They are scattered less hence travel through longer distances 

Applications- 

1) In physical therapy, i.e, to treat muscular strain 

2) To provide electrical energy to satellite by using solar cells

3) For producing dehydrated fruits

4) In greenhouse to keep the plants warm

5) In weather forecasting through infrared photography

6) for taking photographs during the conditions of fog smoke etc

7) In revealing the secret writings on the ancient walls

8) In checking the purity of chemicals and in the study of molecular structure by taking infrared absorption spectrum

9) Infrared rays from the sun keep the earth warm and hence help to sustain life on earth

4) Visible light- 

Frequency range- 4x 10^14 Hz to 8 x 10^14 Hz

Detected by human eye

Produced due to atomic excitation 

Visible light provides information about world surrounding us

5) Ultraviolet rays

Range - 8 x 10^14 Hz to 5 x 10^16 Hz 

Discovered by - Ritter in 1801

Produced by- sun, special lamps and very hot bodies. Can be produced by the arcs of mercury and iron and also can be obtained by passing discharge through hydrogen and xenon

Properties- 

1) Obey laws of reflection and refraction

2) They can also undergo interference and can be polarised

3) When allowed to fall on metals they cause the emission of photoelectrons

4) They can affect a photographic plate

5) These rays can cause fluorescence  in certain materials

6) They cannot pass through glass but quartz, fluorite and rocksalt are transparent to them.

Uses- 

1) For checking the mineral samples through the property of ultraviolet rays causing fluorescence 

2) In the study of molecular structure and arrangement of electrons in the external shell through ultraviolet absorption spectra

3) To destroy the bacteria and for sterilizing the surgical instruments

4) Can cause photoelectric effect and hence are used in burglar alarms

5) In the detection of forged documents, fingerprints in forensic laboratory

6) To preserve food stuff

6) X-rays

Range- 10^16 - 3x 10^19 Hz 

Discovered by- accidentally by German professor W. Rontgen in 1895 

Produced by - When high energy electrons are stopped suddenly on a metal of high atomic number x-rays are produced. Using Coolidge X-ray tube

Properties- 

1) Have very short wavelength ranging from 0.01 Angstrom to 10 Angstrom

2) They are not deviated by electric and magnetic fields

3) They affect the photographic plate very intensely

4) They ionise the gas through which they pass

5) They cause fluorescence in substance like zinc sulphide, barium platino- cyanide, calcium tungstate, etc.

6) They can also cause photoelectric effect

7) Have high penetrating power

8) They travel in straight line and while doing so they cast a shadow of object falling in their path

9) Can undergo reflection, refraction, interference, deflection and polarisation

10) Have injurious effect on human bodies exposure of human body to x-ray cause reddening of skin

11) When x-rays fall on certain material secondary x-rays are produced which are characteristic of the metal

Uses- 

1) In surgery for the detection of fractures, foreign bodies like bullet, diseased organs and stones in the human body

2) In engineering for detecting faults, cracks, flaws and holes in final metal products and also for testing of weldings, castings and moulds

3) In radiotherapy to cure untraceable skin diseases and malignant growths 

4) In detective department for detection of explosives, opium, gold and silver in the body of smugglers

5) In industries for the detection of pearls in oysters and effects in rubber tyres, gold and tennis balls etc and also for testing the uniformity of insulating material

6) In scientific research for the investigation of structure of crystals, arrangement of atoms and molecules in the complex substances

7) Gamma rays

Range- 3 x 10^18 Hz to 5 x 10^22

Discovered by - Rutherford

Detected with - Geiger counter

Emitted from - nuclei of some radioactive elements 

Properties- 

1) These rays are highly penetrating and can penetrate through several centimetres thick iron and lead blocks

2) They have got a small ionising power

3) They can affect a photographic plate

4) They are not deflected by electric and magnetic fields

5) Gamma rays knockout electrons from the surface on which  they fall

6) They produce heating effect in the surface exposed to them

Applications- 

1) Used in radiotherapy and in hospitals to treat cancer and tumours

2) To preserve the food stuffs for a long time as the soft gamma rays can kill microorganisms easily

3) To produce nuclear reactions

4) To provide valuable information about the structure of atomic nucleus