Then from law of conservation of energy. Let V be the potential difference between anode and cathode, then the potential energy is eV. Since the cathode rays (electron beam) are accelerated from cathode to anode, the potential energy of the electron beam at the cathode is converted into kinetic energy of the electron beam at the anode. i.e the magnitude of electric force is balanced by the magnitude of force due to the magnetic field.Įlectric force balances the magnetic force – the path of the electron beam is a straight line. Thomson, led to the discovery of the negatively charged part of the atom, the electron. For a fixed electric field between the plates, the magnetic field is adjusted such that the cathode rays (electron beam) strike at the original position O The cathode ray tube experiment, originally carried out by J.J. He demonstrated that cathode rays were negatively. Determination of velocity of cathode rays: Thomson discovered the electron by experimenting with a Crookes, or cathode ray, tube. When Thompson conducted his cathode ray experiment, how did he know that the negatively charged electrons were so small He knew that they were deflected in measurable ways by electric and magnetic fields, so he concluded that they must have a very small mass to charge (m/e) ratio. Thomson added a positively charged plate on one side of the cathode ray and a negatively charged plate on the other side, he observed a large deflection towards the positive plate, and a small deflection towards the negative plate (see image below). What is the speed of the electrons as they leave the 380 V plate. In this MIT lecture, at 7:22, the professor says that when J.J. 1) The electron beam is produced by accelerating electrons through an electric potential difference of 380 V. This is achieved by coating the screen with zinc sulphide. Cathode Ray Tubes and The JJ Thompson Experiment. When the cathode rays strike the screen, they produce scintillation and hence bright spot is observed. Further, this gas discharge tube is kept in between pole pieces of magnet such that both electric and magnetic fields are perpendicular to each other. These cathode rays are now allowed to pass through the parallel metal plates, maintained at high voltage. An anode disc is made with pin hole in order to allow only a narrow beam of cathode rays. A highly evacuated discharge tube is used and cathode rays (electron beam) produced at the cathode are attracted towards anode disc A. 
Thomson experiment to determine the specific charge of an electron In the presence of electric and magnetic fields, the cathode rays are deflected.Īrrangement of J.J. Thomsons work on gaseous discharge, University of Bath, 1985, in which further details may be found.Group Activity On Biography Of A Nobel Prize Winning Physicist J.J.Thomson Submitted to : Dr.
The specific charge is defined as the charge per unit mass of the particle. Matter and the Atomic Theory FatimaCarino23.Thomson measured the specific charge (e/m) of electron.
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