Explanation of Photoelectric Effect and their Laws.

 Explanation for the Photoelectric Effect :

The experimentally observed facts of photoelectric effect can be explained the help of Einstein's photoelectric equation.

i) Each incident photon liberates one electron, then the increase of intensity of the light (the number of photons per unit area per unit time) increases the number of electrons emitted thereby increasing the photocurrent, The same has been experimentally observed.

ii) From K(max)=h v—Φ•, it is evident max that K is proportional to the frequency max of the incident light and is independent of intensity of the light.

iii) There must be minimum energy (equal to the work function of the metal) for incident photons to liberate electrons from the metal surface. ( h v= h v 1/2 mv^2 ). 

Below this value of energy, emission of electrons is not possible. Correspondingly, there exists minimum frequency called threshold frequency below which there is no photoelectric emission.

iv) According to quantum concept, the transfer of photon energy to the electrons is instantaneous so that there is no time lag between incidence of photons and ejection of electrons. Thus, the photoelectric effect is explained on the basis of quantum concept of light.

Laws of Photoelectric Effect :

i) For a given metallic surface, the emission of photoelectrons takes place only if the frequency of incident light is greater than a certain minimum frequency called the threshold frequency.

ii) For a given frequency of incident light above threshold value, the number of photoelectrons emitted is directly proportional to the intensity of the incident light. The saturation current is also directly proportional to the intensity of incident light. 

iii) Maximum kinetic energy of the photo electrons is independent of intensity of the incident light.

iv) Maximum kinetic energy of the photo electrons from a given metal is directly proportional to the frequency of incident light.

v) There is no time lag between incidence of light and ejection of photoelectrons. 

" When you change the way you look at things, the things you look at change. "

--- Max Planck.---  

What is Space?

Space holds many secrets. It contains places  where human beings can be stretched into spaghetti shapes, or boiled, or frozen solid: that's  why astronauts wear protective clothing in the  space. 

Welcome to a mysterious — and endlessly fascinating — world. 

♦ What is space?

                               When people think of space,  they think of:

                      ♠ Weightlessness — everything  floats as if there's no gravity.

                       ♠ Nothingness — vast areas of  space are completely empty.

                        ♠ Stars —  every star is a burning ball of gas. Our Sun is a star.

                         ♠  Astronauts — people who  explore the world beyond our Earth.

                          ♠ Rockets and Satellites — These  are what scientists use to explore space.

                           ♠ Silence — there is no air in  space, so there is absolutely no sound.

 

♦ Is that space?

                              On a cloudless night, you can see  thousands of stars. Space is the name we give to  the huge empty areas in between the  atmospheres of stars and planets. Apart from the odd rock, space is sprinkled only with dust and  gas.

♦ Why is space so dark?

                                            Space is black because  there is nothing there to reflect light. From space,  Earth looks lit up because light from our Sun  reflects off sea, and land, and the particles in our  atmosphere.

♦ How the distance is measure in space?

                                                                         The  distance measure in space in light years. One light year is the distance light travels in one year: that's  10 million million km ( 6 million million miles ). 

♦ Is anyone there?

                                  • If there are aliens, it is unlikely they will speak the languages of Earth, so  communication may be a problem. Coded signals  have been sent into space. People are also  listening for signals from space.

           

                                   • SETI ( The search for Extra Terrestrial Intelligence ) uses powerful radio  telescopes to scan for alien signals. However, so  far nothing has been found. 

         

                                   • Message into space:

                                                                         In 1974,

 astronomers at Arecibo, Puerto Rico, sent a radio  message from us to the stars. It was sent towards 

a cluster of stars called M13, where it will arrive  in 25,000 years. We may then get a reply after  another 25,000 years.( Is anyone there to read it ! )

                                    

 The Arecibo message lasts  three minutes. It is consists of 1,679 pulses,  which when arranged from a pictogram. The  pictogram explains the basis of life.

♦ Is a black hole may be a doorway to another  universe?

                 Some people think a black hole may be a doorway to another universe. But it's all just  speculation. Nobody really knows. However, it is  doubtful someone could survive the journey  through the hole to find out. An astronaut unfortunate enough to try would be stretched out  like a piece of spaghetti... 

            

              ♥ “ Two Possibilities Exist: Either We Are  Alone In The Universe Or We Are Not. Both Are Equally Terrifying. ”

                                — Arthur C. Clark.