Biripali

Radioactivity: The uranium salt emitted the rays spontaneously.The phenomenon of spontaneous emission of radiations by heavy elements is called Radioactivity . Properties of nuclear radiation: 1. Properties of Alpha(α) rays: - Alpha(α) particles is a helium nucleus consisting of two protons and two neutrons. - The velocity of α- particles ranges from 1.4 x 10^7 m/s to 2.05 x 10^7 m/s. -They are deflected by electric and magnetic fields. - Alpha (α) particles produce fluorescence in substance like zinc sulphide and barium platinocyanide. - They are massive particles and hence easily stopped by an aluminium sheet of only 0.02mm thick or even by ordinary sheet of paper. - They have great ionising power. Each α-particles produces thousands of ions pairs in a gas before being absorbed. - They get scattered while passing through this metal foils. - They affect a photographic plate. - They can produce artificial radioactivity in certain elements and can produce nuclea...

Planks quantum Theory:    To explain the black body radiation Plank assumed that the energy of oscillatory particles should be discrete rather then continues. According to him the oscillators can emit or absorb energy in the packets. - Energy carried by each photon is hv . - E=n h v where n= 1,2,3,..... h is a planks constant.The value of h=6.625 × 10^−34 J.s Thus photons are particles of electromagnetic radiation emitted by source of radiation . The important characteristics of photons are: 1. Energy of photons is E=hv = hc/λ, where v is frequency of photons and c is velocity of radiation. 2. All photons travel with the same speed which is equal to speed of light i.e c =3 x 10^8 m/s. 3. The speed of photons is different in different media. 4. Photons of different wavelengths (λ) move with different speeds in the same medium. 5 .The photons travels in straight lines. 6 .Rest mass of photon is zero. 7. Momentum of a photon= Mass x velocity ...

Black body Radiation: Every body emits energy in the form of wave due to its temperature these radiation are known as Thermal radiation . -A perfectly blackbody is one which absorbed heat radiation of all wavelength incident on it. -It neither reflects nor transmits any of the incident radiation and therefore,appears black. - When a black body is heated its emits radiation which are known as black body radiation.

Photoelectric effect: when light is incident on a metal surface then electrons are emitted from it. This phenomena is called photoelectric effect.The emitted electrons are called photoelectrons. Laws of photoelectric emissions : 1. The emission of photo-electrons takes place only when the frequency of incident radiation is above certain critical value of that metal.This critical value is called threshold frequency . 2 . The emission of photo-electrons starts as soon as the light falls on metal surface i.e.the photoelectric emission is instantaneous. 3 . The maximum kinetic energy with which the photo-electrons are emitted from a metal surface is independent of the intensity of the light and only depends upon the frequency. 4 . For a given frequency, the number of photo-electrons emitted is directly proportional to the intensity of incident light . 5 .The energy distribution of the photo-electron is independent of the intensity of the incident ...

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