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In an evacuated glass tube fitted with electrodes, the negative electrode is called the cathode and the positive electrode is called the anode. The rays that were being emitted by the cathode and travelled to the opposite end of the tube through one or more screens are called cathode rays. By observing the direction in which these rays were deflected by electric and magnetic fields, scientists concluded that the rays were negatively charged. In 1897, J. J. Thompson (1856-1940) was able to directly measure the charge to mass ratio, e/m, for cathode rays. In Thompson's apparatus, cathode rays were accelerated by a high voltage and allowed to pass between a pair of parallel plates into the tube. The cathode rays passed through parallel plates that could cause the rays to be deflected in one direction (for example upwards). A current placed through coils produced a magnetic field that caused the rays to be deflected in the opposite direction. By balancing the electric and magnetic force on charged particles, the velocity of the cathode rays could be found. Fe = eE, and Fg = evB, therefore E vV= B If the cathode rays passed through a magnetic field only, then they followed a curved path. The centripetal force on the rays were brought about by the magnetic field. 2 Fe = evB and Fzmv , Y 2 myv therefore ., p R This simplifies to B = n R The charge to mass ratio can therefore be found: L . The cathode rays soon came to be called electrons. m BR A mass spectrometer can be used to find the mass of charged patrticles. lons are produced by heating, or by an electric current, at a source. They enter a region where electric fields and magnetic fields are perpendicular to each other. Only those ions whose speed is ,, :EB will pass through undeflected. In the second region, there is only a magnetic field B', and the ions follow a circular path. The ions expose a photographic plate where 2 they strike, and thus the radius of motion can be measured. In this region qu'= MV The mass of the charged particles can therefore be found R _gBBR using z, Atoms of the same element that have different masses are called isotopes. An atomic mass unit (u) is ocne-twelfth the mass of the carbon isotope 12C. The equivalent mass in kilograms is 1 u = 1.66 x 1027 kg. Question(s): The physics of chlorine isotopes and the mass spectrograph. The isotope 33C| has a mass of 5.80 x 10726 kg and a negative charge of 1.60 x 10 19 C. It is accelerated through a potential difference of 250.0 V and deflected by a magnetic field of 2.00 T. 1. What speed does the ion acquire as it accelerates? 2. What is the radius of curvature of this ion? 3. If a heavier isotope of chlorine is used but one with the same charge, would the radius of curvature be larger or smaller. Explain your reasoning by referring to the equation you used to determine the radius in the previous