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^ γ-rays

 – rays

(a) Produced in nuclear reactions and are also emitted by radioactive nuclei (such as Co 60 & Cs 137).

(b) Properties: Effect on photographic plate, fluorescence, ionization, diffraction, high penetrating power & can cause serious damage if absorbed by living tissues.

(c) Used

  1. in radio therapy to treat certain cancers and tumors
  2. to produce nuclear reactions
  3. to study the atomic nuclei.

^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.

*Uniform motion

*Uniform motion

Uniform motion means uniform velocity i.e. both the speed & the direction remain same w.r.t. time.

This is the case when the net force acting on it is zero or   of body is zero. This case is also called dynamic equilibrium.

  1. For uniform motion average speed is equal to instantaneous velocity.
  2. A body can never have a uniform velocity but a varying speed.

^Displacement versus distance

^Displacement versus distance

  Displacement Distance
Between two points Length of shortest path Length of actual path
Sign     +ve or –ve +ve always
Can be zero Yes No
Direction Initial to final Meaningless
SI unit meters meters
Are equal Only for motion along straight line with no reversal

^A long horizontal fixed wire carries a current of 100 A. Directly above and parallel to it is another wire carrying a current of 20 A and weighing 0.04 N/m.

^A long horizontal fixed wire carries a current of 100 A. Directly above and parallel to it is another wire carrying a current of 20 A and weighing 0.04 N/m. The separation between the two wires so that the upper wire is just supported by the magnetic repulsion is

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