Monday, 25 April 2016

Hallwachs Experimental Setup and Explanation

Hallwachs Experimentset-up

Experimentset-up to study the photo electric effect is shown  in  Fig. It  consists  of  an  evacuated quartz  bulb  with  two  zinc  plates  cathode and  anode.  The  plates  are  connected  to  a battery  and  a  sensitive  galvanometer.  In  the absence   of   any   radiation   incident   on   the plates.There  is  no  flow  of  current  and  hence there  is  no  deflection  in  the  galvanometer. But,when  an  electro  magnetic  radiation  like ultraviolet  radiation  is  allowed  to  fall  on  the cathode plate which  is  connected  to  the  negative terminal  of  the  battery, a  current  begins  to flow,indicated  by  the deflection  in  the  galvanometer But,  when  ultraviolet  radiation  is made  to fall  on  anode there  is  no  deflection  in  the  galvanometer.  These observations reveal that the particles emitted by the cathode plate  due to the photoelectric  effect  are  negatively  charged.  These  particles  were  found to  be  electrons.  The  observed  current  known  as  the  photoelectric current  is  due  to  the  flow  of  electrons.After  the  study  of  photoelectric  effect  by  Hallwachs,  scientists J.J.Thomson, Lenard, Richardson, Compton did a series of experiments to  study  the relationship  between  photoelectric  current,  intensity  ofincident   radiation,   velocity   and   the   kinetic   energy   of   the   photo electrons,   and   their   dependence   on   the   wave   length   of   incident radiation used.