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Thermionic Emission and Cathode Rays

Thermionic Emission and Cathode Rays. Physics- Ms. Yuli. Hafiz, Chelsea, Qwensie and Hendy. Contents. What is Thermionic Emission? What is Cathode Ray?. Before we begin…. Anode: a positively charged electrode. Cathode: a negatively charged electrode. Thermionic Emission.

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Thermionic Emission and Cathode Rays

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  1. Thermionic Emission and Cathode Rays Physics- Ms. Yuli Hafiz, Chelsea, Qwensie and Hendy

  2. Contents • What is Thermionic Emission? • What is Cathode Ray?

  3. Before we begin… • Anode: a positively charged electrode. • Cathode: a negatively charged electrode.

  4. Thermionic Emission • Thermionic emission is a process where heat energy moves electrons through a surface.

  5. Why does it happen? • British physicist Owen Willans Richardson discovered that in any solid metal, there are one or two electrons per atom that are free to move between atoms. • Occasionally, some electrons would gain enough velocity to exit the metal without returning.

  6. How does it happen? • When we heat up the metal, the electrons gain more kinetic energy. • Sometimes, this is enough for the electrons to “leap out” of the metal. • However, losing electrons would cause the metal to become positively charged~ • This causes an electrostatic attraction between the metal and the “free” electrons. • In the end, the system is neutrally charged! >>>:D

  7. How is it used? • The heated metal can be used as a cathode. In this context, it would be called a hot cathode. • Thermionic emission is used to help cooling or generating power. Vacuum tubes and solid-state devices are often used to create the thermionic movement of electrons. • The concept was first utilised by Thomas Edison in 1880. While working on his incandescent light bulb, he noticed that certain parts remained dark. This allowed him to identify the flow of electrons due to heat, resulting in the creation of the diode.

  8. Cathode Ray • A cathode ray is a beam of electrons that travel from the negatively charged to positively charged. • In the late 1800s, physicist Phillip von Lenard studied the cathode rays intently and his work earned him the 1905 Nobel Prize in Physics.

  9. Why and how does it happen? • In a vacuum tube, the cathode repels electrons while the anode attracts them. • As a result, the electrons travel down the tube from the cathode to the anode.

  10. How do we use it? • The most popular commercial application of cathode ray technology is in TV and computer screens. • Cathode rays are fired through vacuum tubes to light up the phosphor on the screen.

  11. Sources • WiseGeek.com • About.com – Physics • University of St. Andrews Official Site

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