He assumed that cathode rays were negatively charged particles and he used apparatus similar to that used by William Crookes to observe the properties of cathode rays. Thomson set out to measure the charge-to-mass ratio (q/m) for an electron. Cathode rays are identical: regardless of the type of material used as the cathode all cathode rays are identical.Cathode rays carry and are able to transfer momentum: When a cathode ray strikes a CRT containing a paddle wheel, some of their momentum is transferred to the paddle, which makes the paddle wheel roll in the same direction that the cathode rays are travelling.Cathode rays can be deflected by magnetic fields: When a pair of bar magnets is placed next to the cathode ray tube, the cathode rays are deflected as predicted for negatively charged particles by the right-hand rule.Cathode rays can be deflected by electric fields: When charged plates are placed either side of a CRT, the cathode rays are deflected in the direction opposite to that of the electric field.Cathode rays are also able to cause the wall of the glass tube to glow. Cathode rays can cause fluorescence: As a cathode ray passes from the cathode to the anode, it causes the fluorescent material to fluoresce, leaving a clear trace of the path the cathode ray has taken.Cathode rays travel in straight lines and originate at the cathode: A CRT that contains a maltese cross will be illuminated from the cathode end and cast a defined shadow at the other end of the tube.With the development of effective CRT, William Crookes amongst others, began to investigate the nature and behaviour of the cathode rays.
High voltage: Extremely high voltage is required to give the electrons enough kinetic energy to make their way to the anode. The low pressure ensures that as the cathode rays make their way from the cathode to the anode there will be minimal collisions between the air molecules inside the tube and the electrons (cathode rays). Low gas pressure: A CRT must have very low gas pressure – close to vacuum. When the power is on, the cathode rays are observed to flow from the negative cathode to the positive anode inside the tube. The electrode connected to the negative terminal of the power source is named the cathode, while the electrode connected to the positive terminal is named the anode. The two electrodes are connected to a power source via an induction coil to produce a sufficiently high enough voltage. These observations led to the discovery of the electron.Ī cathode ray tube CRT consists of an evacuated glass tube and two metal electrodes, one at each end of the glass tube. Cathode ray tubes improved until William Crookes developed a CRT which produced a very strong and consistent beam of cathode rays which allowed for their properties to be studied. The Existence and Properties of the Electron – LearnĬathode rays were studied by observing their behaviour in cathode ray tubes (CRT).
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