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Modern Physics CATHODE RAYS
Greetings! I am your educator- Udit Gupta. In this first lesson, we will learn how modern physics came into existence. We will study about cathode rays and its properties. For more such courses and lessons: https://unacademy.com/user/udit13
Cathode Rays . If the pressure of the gas in a discharge tube is lowered and it is connected across a high voltage, the walls of the tube start to glow, indicating that something is coming out of the cathode, travelling through the length of the tube before falling on the walls. . This is actually a stream of fast moving electrons. . This fact was recognized after a series of experiments carried out by Crookes, Thomson and others. They named these invisible streams coming from the cathode as Cathode rays and established the following main properties.
Cathode Rays Cathode rays are emitted normally from the cathode surface Their direction is independent of the position of the anode. . This can be shown by taking the cathode in the shape of a concave surface. . If a fluorescent material is placed at the centre of curvature of the cathode surface, the material glows with maximum intensity Any lateral shift reduces the glow
Cathode Rays . Cathode rays travel in straight lines. . This can be shown by placing a metal cross in the path of cathode rays . A shadow appears on the wall on the opposite side as the cathode rays do not reach there (there is no fluorescence in the shadow region) . If the cross is lowered, the shadow disappears.
Cathode Rays . Cathode rays exert mechanical force on the object they strike. . To show this, one can put a light wheel of mica in the path of the cathode rays. With proper arrangement, the wheel starts rotating as the cathode rays fall on it.
Cathode Rays . Cathode rays produce heat when they strike a material surface . If a blackened platinum strip is placed at the centre of curvature of a concave-shaped cathode. The strip becomes red-hot after some time. Cathode rays produce fluorescence when they strike a number of crystals, minerals and salts. . When cathode ray strike a solid object, specially a metal, X-rays are emitted from the object.
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