ELECTRO MAGNETIC SPECTRUM

1. Spectrum:-
A spectrum is a group of wave lengths or frequencies.

2. Electro Magnetic Waves:-
The waves traveling with the velocity of light and consisting of oscillating electric and magnetic fields perpendicular to each other and also perpendicular to the direction of their propagation are called electro magnetic waves.

3. Electro Magnetic Radiations:-
Electro magnetic radiations are characterized by oscillating electric and magnetic fields perpendicular to each other and perpendicular to the direction of propagation.

4. Types of electro magnetic radiations:-
The various types of electro magnetic radiations are
1. visible spectrum.
2. Infra Red spectrum(IR)
3. Micro waves.
4. Radio Waves.
5. Ultra violet radiation.
6. X-rays.
7. γ-rays.

5. Mention the uses of radio waves
Radio waves are used in radio astronomy. They are also used in ordinary radio transmission.

6. What is
a) Radiography
Medical diagnosis using soft X-rays is called radiography.
b) Radio therapy
The cure of a disease using soft X-rays is called Radio therapy.
c)Radio astronomy
Mapping of the radio emissions from extra-terrestrial sources is known as ‘radio astronomy’.

7. What is visible spectrum
The set of colours from violet to red i.e., VIBGYOR is called visible spectrum.

8. The atmospheric ozone is depleted in recent years. Why
Atmospheric ozone is depleted in recent years as a result of chemical reactions with chloro fluoro carbons realsed from aerosol sprays, refrigeration equipments and other pollutants.

9. What is thermopile
A sensitive instrument used to measure a very small temperature is called a thermopile.

10. How are infra red radiations detected
Infra red radiations are detected by thermopile, thermometer and bolometer.

11. Harmful effects of ultra violet radiations:-
Brief exposure causes common sun burns and long term exposure leads to skin cancer.

12. Which layer is protecting living beings from ultra violet radiations
Ozone layer.

13. Mention the causes for depletions of ozone layer
Chemical reactions with chloro fluoro carbons released from aerosol sprays, refrigeration equipments and other pollutants causes depletions of ozone layer.

14. Discuss the types of electro magnetic radiations? Mention their wave lengths
(or)
How are electro magnetic radiations produced ? Write their applications

Types of radiations(spectrum) Range of wave  length Production source Applications/uses.
1. Visible spectrum 0.4μm-0.7μm It is emitted when excited valence electrons in atoms jump back to their normal states. Light emitted from  sun and distant stars give information about the composition of matter present in them.
2. Infra red spectrum 0.7μm-100μm These are emitted by molecules when they change their states of rotational (or) vibrational motion.  Heat from hot bodies travel in the form of infra red radiations and there fore all the heat bodies form sources of Infrared radiations

 

 

 

Infrared radiations are used in physiotherapy.  Infrared radiations are also used  to take photographs of objects in darkness.
3. Microwaves 10μm-10m These waves are produced  by electro magnetic  oscillators with high frequency 109-1011 c/s)  in electric circuits. Micro waves are often used in RADAR, telemetry and micro wave ovens.  These are also used to transmit telephone conversations satellite communications also utilize microwaves.
4. Radio waves 1m-100km These are produced by electro magnetic oscillators of low frequency.  These radiations are created when electrons are accelerated in an electronic circuit. They can travel long distances carrying messages.  These are also received from extra terrestrial sources.  Mapping of radio emissions from extra terrestrial sources is known as radio astronomy.
5.  Ultra violet spectrum 0.4μm-1nm These radiations are produced by the transitions  of electrons in an atom Only a little of ultra violet radiations reaches the ground.  We are protected from the ultra violet radiations of the sun because of ozone layer in outer atmosphere.  This layer absorbs u.v rays strongly.
6.X-rays 10nm-0.001 nm

(100 -0.01)

These are produced in discrete wavelengths, in individual transition among the inner electrons of atom.  X-rays In continuous  wave lengths can also be produced when incident electrons are decelerated inside the target atoms. Soft X-rays are used in medical diagnosis called  radio graphy.  These are used to cure some diseases.  This method is called radio therapy.
7.  γ rays 0.1nm-0.0001nm

(1-0.001)

These are emitted in radio activity. Exposure to intense γ-radiations leads to harmful effects on human body.  These are the most penetrating  electro magnetic rations.(causes genetic changes-mutations in human body).

15. Mention the most penetrating electro magnetic radiation
γ rays (gamma rays)

16. Mention the uses of infrared radiations
1. It is used in physiotherapy.
2. It is used in taking photographs of objects in darkness.

17. Mention the uses of micro waves
1. Micro waves are used in RADAR, telemetry and micro wave ovens.
2. Used to transmit telephone conversations.
3. Used in satellite communications.

18. Draw a diagram of dispersion of white light through a prism


19. Draw a sketch of how electro magnetic radiations are produced due to oscillating electric and magnetic fields
Or
Draw a neat diagram of electro magnetic waves and label the parts

E – Oscillating Electric Field Vector, B – Oscillating Magnetic Field Vector

20. Draw a diagram of different regions of electro magnetic waves of increasing order of wavelengths

Various regions of EM spectrum and their wavelength ranges.

1. Visible spectrum 2. IR Spectrum 3.Micro waves 4. Radio waves
5. UV spectrum 6. X-rays 7. γ- Rays

III Match the following:-

          A                                                     B

1. UV radiations                          (c) a)100 -0.01 (10nm-0.001nm)

2. Infra red                                 (g) b) 0.001 -1 (0.1nm-0.0001nm)

3. X-rays                                     (a) c)1nm-0.4μ

4. Radio waves                           (e) d)10μm-10m

5. γ-rays                                     (b) e)1m-100km.

6. Micro waves                           (d) f)0.4μm-0.7μm

7. visible spectrum                     (f) g)0.7μm-100μm.

2.          A                                                  B
1. Hot                                          (d) a)VIBYGOR

2. Telemetry                                 (e) b)skin diseases

3. UV radiations                            (b) c)Radio therapy

4. White rays                                 (a) d)IR radiations.

5. X-rays                                        (c) e)Micro waves.

III. Fill in the blanks:-

1. A variety of glass that can absorb infra red radiations is                 (c).
a)Bohinium glass                                     b)Flint glass.
c)Soda glass.                                            d)Borosilicate glass

2. Prisms are made up of rock salt materials which are used to detect Infra red radiations.

3. Infra red radiations are from a class of waves called                        (d)
a) photo electric effect                             c)electro magnetic induction
b visible spectrum                                    d)electro magnetic spectrum.
4. All electro magnetic waves are transverse in nature.

5. If ‘c’ is the speed of light in vacuum the related frequency of electro magnetic wave is ‘n’ and wave length is λ then c=nλ.

6. The value of velocity of light in vacuum is 3X108m/s.

7. When the valence electrons jump to their normal state of an atom the spectrum emitted is called visible spectrum.

8. The color of light emitted by a particular substance is a characteristic of atoms in a substance.

9. The radiations whose wave lengths are larger than those of visible light are called infrared radiations.

10. The radiation that can be detected by thermopile, thermometer are infra red radiations.

11. IR radiations find applications in                                                    (d)

12. The radiations which can be used to take photographs of objects in darkness is infrared radiations.

13. The waves that are commonly produced by electro magnetic radiations of high frequency in electric circuits are micro waves.

14. The value of high frequency of an electro magnetic oscillator used to produce micro waves is

15. The electro magnetic radiations used in micro wave ovens are micro waves.

16. Micro waves are often used in                                                        (d)
a)sonal                                                           b)laser
c)masar                                                          d)RADAR.

17. In satellite communications micro waves are used.

18. The radiations that are created when electrons are accelerated in an Arial are radio waves.

19. Radio astronomy has provided information about the universe which is not obtainable using                                                                                  (c)
a)Terrestrial telescope b)electron microscope.
c)optical telescope d)binoculars.

20. The wave length of UV radiations from 0.4μm-1nm.

21. Mapping of the radio emissions from extra terrestrial sources is called radio astronomy.

22. Layer of the atmosphere that protects our body from hazards of UV rays is ozone layer.

23. Atmospheric ozone is depleted in recent years as a result of chemical reactions with chloro fluoro carbons.

24. The rays that are produced when electrons are decelerated are X-rays.

25. Hard X-rays are used in testing materials in industries.

26. X-rays cannot pass through                                                             (d)
a)tissue of a human body.                 b)wood of few mm thickness.
c)glass.                                               d)bones.

27. The process of using X-rays in medical diagnosis is radiography.

28. Wave length of X-rays range from 10nm-0.001nm.

29. The process of curing certain diseases using X-rays is called radio therapy.

30. Radiations of shortest wavelength are gamma rays (also high frequency).

31. Radiations emitted when an excited nucleus comes to its ground state is called gamma rays(γ).

32. The rays that are produced in the decay of certain particles is gamma rays(γ)

33. Most penetrating radiations are gamma rays(γ).

34. 1angstrom =10-8 cm or 10-10m.

35. Exposure to intense gamma (γ) radiations lead to harmful effects of human body.

36. When a ray of sunlight falls on a prism, the transmitted light produces a sequence of colors called visible spectrum.

37. Spectrum is a group of wavelengths or frequencies.

38. Visible spectrum is a group of seven colours band.
39. The radiations detected to the right of the red radiations are infrared radiations.

40. Infrared radiations are similar to these found towards the right of the red radiations.

41. Ordinary soda glass is known to absorb infrared radiation.

42. Prism of rock salt are used for detection of IR radiations.

43. The different types of radiations including IR, visible ,UV radiations form a class of waves are called electro magnetic waves.

44. The radiations detected on the left of visible spectrum are called ultra violet radiation.
45. The different radiations can be described in the terms of oscillating, electric and magnetic fields perpendicular to each other are called electro magnetic radiations.

46. The electro magnetic radiations travel with the same speed i.e., the speed of light in vacuum (3X108m/s).

47. The relation showing the velocity of electro magnetic waves (C) and frequency (n) and wavelength(λ) is c=n λ

48. All the known sources of light emit visible spectrum.

49. Wavelength of visible spectrum extends from 0.4μm to 0.7μm.

50. Visible spectrum is emitted when the excited valance electrons in an atom jumps to their normal state.

51. The light emitted by the sun and distant stars gives information about the composition of matter of them.

52. Infrared radiations have wave lengths larger than that of visible light.

53. Infrared rays can be detected by the devices like thermometer, thermopile, bolometer etc.,.

54. Infrared radiations find applications in physiotherapy.

55. Infrared radiations are used to take photographs of objects in darkness.

56. Microwaves are electro magnetic waves with the wavelengths in the range of 10μm-10m.
57. Microwaves are produced by electro magnetic oscillators of high frequency in electric circuits.

58. Micro waves are often used in RADAR.

59. RADAR means radio detection and ranging.

60. The waves of electro magnetic nature that are used in micro wave ovens are micro waves.

61. Micro waves are used to transmit telephone conversations.
62. Satellite communications makes use of micro waves.
63. Radio waves have wavelengths ranging from 1m-100km.
64. Radio waves are produced by electro magnetic oscillators of low frequency.
65. Radio waves are created when electrons are accelerated in the receiver.
66. Radio waves are also received from extra terrestrial sources.
67. Radio astronomy has provided information about the universe which is not obtainable using an optical telescope.

68. The radiations of wave length shorter than the visible light are called ultra violet radiations.

69. The ultra violet radiations are received from the sun.

70. Ultra violet radiations are produced by the transition of electrons in atoms.

71. Brief exposure to the UV rays causes sun burns.

72. Long term exposure to UV rays causes skin diseases including skin cancer.

73. We are protected from UV radiations the sun because of the sun because of ozone layer in the atmosphere which absorbs UV rays strongly.

74. Ozone layer is depleted in recent years as a result of chloro fluoro hydro carbons released from aerosol sprays and refrigeration equipments.

75. X-rays are produced in discrete wavelengths in individual transition among the inner electrons of atom.

76. X-rays in continuous wavelengths are produced when electrons are decelerated.

77. X-rays of shorter wavelengths are called hard X-rays.

78. Hard X-rays are used to determine testing materials in Industries.

79. Hard X-rays are used to determine the spacing between the atoms in a crystalline solid.

80. X-rays of longer wavelength can easily penetrate through tissues of human body.

81. X-rays cannot penetrate through bones and other solid materials.

82. Soft X-rays are used in medical diagnosis is called radiography.

83. X-rays are used to cure some diseases and is called radio therapy.

84. γ-rays are electro magnetic radiations with shortest wave length.

85. The wavelength of γ –rays ranges from 1 -0.001 or 0.1nm-0.0001nm.
86. Example of natural radio active substance is 92U235 (Uranium).

87. 92U235 emits γ( gamma ) radiations.

88. Gamma radiations are emitted when excited nucleus comes to ground state.

89. γ-rays are produced in the decay of certain elementary particles.

90. γ-rays are the most penetrating electro magnetic radiation.

91. γ-radiations are emitted when the excited nucleus comes back to ground state.

 

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