Thermionic Emission Flashcards
What is thermionic emission?
This is the process by which electrons are emitted from a hot metal surface
How Can electrons be produced?
- thermionic emissions
- Photo electric emissions
In What devices are some unique emissions applied in?
Diode valves, cathode ray tube, cathode ray oscilloscope, x-ray tube.
What is photoelectric emission?
This The process by which electrons are emitted from the metal surface when exposed to electromagnetic waves of sufficient frequency
Where does photoelectric emission occur
Photoelectric cells
What Electrons emitted referred to as?
Photo electrons
What are the electromagnetic waves used called?
Ultraviolet radiations
What is the mechanism of a photoelectric cell?
- electromagnetic radiation is directed to the cathode and supply sufficient energy for electron liberation.
- The anode attracts electrons in the flow of electrons generates current around the circuit deflected by the ammeter.
- The current produced is proportional to the intensity of the radiation.
What is the stream of electrons flowing From the cathode to the anode cold?
Cathode rays
What are some applications of the photoelectric effect?
Burglar, alarms, automatic, lighting systems, Solar calculators, television, cameras, automatic door systems, soundtrack on a film.
What are cathode rays?
Cathode rays are streams of fast moving electrons
How are cathode rays produced?
- The cathode is heated with low-voltage across the heater.
- The cathode emits electrons by thermionic emission.
- The electrons omitted, our accelerated by high-voltage across the heater and the anode increasing the speed of electrons hence forming cathode rays.
- Some of the electrons( cathode rays) pass through the anode and form a parallel beam of electrons, which appears as a spot the fluorescent screen.
What are some properties of cathode rays.
- They travel in a straight line.
- They are negatively charged.
- they form an x-ray when stopped by a heavy metal.
- They are deflected in a magnetic field.
- They are deflected in electric fields.
- They possess momentum and kinetic energy.
- They ionize air and gas molecules.
In what devices are cathode rays applied?
cathode ray oscilloscope, x-rays and Diode
What is a cathode ray oscilloscope?
This is an instrument used to study the current and voltage wave forms
What three major parts does a cathode ray oscilloscope consist of?
Electron gun, deflecting system, fluorescent screen.
What parts of a cathode oscilloscope make up the electron gun?
Heater,Cathode, Cathode grid and anode
What Parts of the cathode ray oscilloscope make up the deflecting system?
Y plates and x plates
What are the functions of each part of the cathode ray oscilloscope?
- Heater- heats the cathode electrically
- Cathode- Emits electrons by thermionic emission.
- Cathode grid- Controls the brightness of the spot formed on the screen by controlling the amount of electrons that reach the anode to the fluorescent screen.
- Anode- Accelerates electrons produced by the cathode .
- Y- plates- deflects electron vertically.
- X- plates- deflects electrons horizontally.
- Fluorescent screen- Is where the bright spot of electrons is formed
What’s are x-rays?
These are electromagnetic waves of short wave length produced when cathode rays are stopped by a metal surface
How are x-rays produced in an x-ray tube?
- The cathode is heated, and electrons are emitted from it by thermionic emission.
- The elections are accelerated to the anode by high-voltage supply, connected across cathode and unload.
- On reaching the target, 99% of the kinetic energy of electrons is changed into heat energy and 1% kinetic energy of electrons is changed to x-rays.
- The heat generated at the target is cooled by cooling fins and conducted.
What are the energy changes that take place in an x-ray tube?
Electrical energy to heat energy to kinetic energy to electromagnetic energy.
