Thomson’s Experiments
Thomson first investigated the magnetic deflection of cathode rays using the apparatus in รูป 6.7
Cathode rays were produced in the side tube on the left in figure 6.7. The rays pass through the anode and into the bell jar, where they were deflected by a magnet. Figure 6.8 shows how a cathode ray be deflected using a magnet.
As the rays were fluorescent, the path of the rays could be inferred by the position of the fluorescent on a square screen in the ball jar. Thomson repeated the experiment, changing a material of the anode and the type of gas in the bell jar each time. However, he found that the deflection of the rays remained the same in each experiment. He suggested that the cathode ray had the same composition, regardless of where they came from. Thomson went on to perform three experiments that led to the discovery of the electrons.