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^Ultraviolet light

^Ultraviolet light

(a) Produced by special lamps like mercury and iron are lamps and by very hot bodies like sun.

(b) Properties: Effect on photographic plate, fluorescence, ionization, highly energetic, tanning of the human skin.

(c) Used

  1. To destroy bacteria and for sterilizing the surgical instruments
  2. In the detection of forged documents finger prints
  3. In burglar alarms etc as they can cause photoelectric effect.
  4. For studying fluorescence
  5. In the study of molecular structure and arrangement of electrons
  6. To prevent the food stuff.

^Visible light

^Visible light

  1. Produced by hot bodies like sun, electric bulbs and tubes etc. as a result of electronic transitions. Our eyes are sensitive to visible light which helps us to collect the information about our surrounding.
  2. Properties: Reflection, refraction, interference, diffraction, polarization, photoelectric effect, photographic action, sensation of sight.

^Infra red waves


^Infra red waves

(a) Also called heat waves & are produced by hot bodies and molecules.

(b) Properties: Heating effect, reflection, refraction, diffraction & propagation through fog.

(c) Used

  1. In taking photographs during the conditions of fog, smoke etc. as these waves are scattered less than visible rays and hence can travel longer distances through atmosphere under fog, smoke etc.
  2. In weather forecasting
  3. In checking the purity of chemicals
  4. In the study of molecular structures
  5. For producing dehydrated fruits
  6. In green houses to keep the plants warm
  7. To provide electrical energy to satellites using solar cells.
  8. To treat muscular strain.
  9. In solar water heaters and cookers.

^Micro waves

^Micro waves

(a) Produced by special vacuum tubes like klystrons & magnetrons. Due to their shorter wavelengths the microwaves don’t spread or bend around the corners of any obstacle coming in their way, hence can be transmitted as beam signals in a particular direction.

(b) Properties: Reflection, refraction, diffraction and polarization.

(c) Used in

  1. Radar systems used in aircraft navigation.
  2. In communication via satellites.
  3. Speed guns to determine speed of moving automobiles, cricket balls etc.
  4. Ovens for cooking
  5. In the study of atomic and molecular structure.

^Isoclinic lines

^Isoclinic lines

Lines joining the places of equal dip (δ).

^Isogonic lines

^Isogonic lines

Lines joining the places of equal declination (θ).

^Magnetic maps

^Magnetic maps

The three magnetic elements are calculated at different places all over the globe & the results obtained are represented on geographical maps. Usually lines are drawn joining all places having same value of a magnetic element. Such maps are called magnetic maps. The commonly used lines on the magnetic maps are:

^Dip & latitude

Dip & latitude

Assuming that terrestrial magnetism is due to a short magnet at the centre of the earth, then at any point on the surface, tan δ = 2 tan λ where δ is dip and λ is the magnetic latitude.

 

^Diamagnetism

Diamagnetism

Diamagnetics are temporary weak magnets posses magnetism only when placed in external magnetising field. It is found in the atoms or molecules having even number of electrons. In the unmagnetized form of a diamagnetic the magnetic moments of the two electrons having same value of principle quantum number ‘n’ have equal & opposite value cancel out, thus producing net zero magnetic moment. However when placed in an external magnetic field the electron having dipole moment opposite to external magnetic field is accelerated & other one retards, producing a net non zero magnetic moment in a direction opposite to the applied magnetic field. Diamagneitcs get repelled weakly by magnetizing fields. Now when external magnetic field is switched off, the magnetic force on electrons again becomes zero, due to which the two magnetic moments again become equal & cancel each other.

^Cause of magnetism

Cause of magnetism

1. Electrons, protons, neutrons all posses magnetic moment due to both orbital & spin motions. This magnetic moment is ultimately responsible for magnetism.

2. due to spin is also called intrinsic magnetic moment or permanent magnetic moment & can be understood using quantum mechanics only.

3. associated with the orbital motion of a charge can be explained even by classical concepts, for it an electron orbiting around a nucleus in a circle  or radius r at a velocity v it is

4. The minimum value of produced due to the orbital motion of an electron around an atomic nucleus is called Bohr magneton (μ).

5. The nuclear magnetic moment typically is much smaller than the electron magnetic moment .

6. Net magnetic moment of an atom is the vector sum of is magnetic moments of all of its electrons, protons & neutrons, both due to orbital motion & as well as spin motion.

7. Generally magnetic moments of atoms are randomly aligned & thus for any volume containing more than several thousand atoms net dipole moment is usually zero (for all types of material, dia, para, ferro).

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