Day 19: Electrostatic Potential Energy & CRT Applications The change in electric potential energy of a charge moving through an electric field The electric potential energy of two charges The electric potential energy of multiple charges The Electron Volt Work Done to Dissemble a Hydrogen Atom Cathode Ray Tube (CRT) Applications

Electric Potential Energy Suppose a point charge q is moved between two points A & B, where the electric potential due to the charge is VA & VB respectively. The change in the electric potential energy of q in the field is: E q A B

Electrostatic Potential Energy In isolation (ie: no electric field), a point charge has no electric potential energy, because there is no force acting on it. If a second charge is brought near the first charge, there is an electrostatic force between them, then the electric potential of the two charges is: This represents the work done by an external force to bring Q2 from ∞ to r1,2 Q1 Q2 r1,2

Electrostatic Potential Energy Now, in a system of three charges, the total potential energy will be the work done to bring all three charges together. Q1 Q2 Q3 r1,2 r2,3 r1,3 Systems of more charges requires terms

The Electron Volt The Electron Volt is a measure of energy to deal with small energies at the atomic level. 1 eV is the energy required by a particle, carrying a charge of q = e, moving through a potential difference of 1.0 volt

The Work Done to Disassemble a Hydrogen Atom (-) r = .529 x 10-10 m (+) The work necessary to remove the electron is equal to the change in total energy of the atom ( energy as an atom vs. the energy of the atom infinitely far apart ΔE = -13.6 eV. This is, in fact, the ionization energy of hydrogen

Cathode Ray Tube (CRT) Application A CRT is the basis of classic television receivers, computer monitors, and oscilloscopes A CRT is based on a simple vacuum tube diode. A negatively charged cathode is heated by a 6.3 V PS to 1000°C, emitting electrons which are attracted to a positive anode (plate), in that direction only. CATHODE

Cathode Ray Tube (CRT) Application A CRT is a device which is based upon the thermionic diode, in which electrons emitted by the cathode are accelerated by a high voltage anode, through a small hole in the anode – thus coins the term “electron gun” The electrons collide with the screen which has a phosphorescent coating, illuminating the screen with a spot

Cathode Ray Tube (CRT) Application Two sets of deflection plates (1-vertical, 1-horizontal) use an applied voltage to steer the electron beam into a sweeping pattern, called raster. A control grid adjusts the brightness of the beam, using a video signal voltage applied to it. An oscilloscope is a piece of electronic equipment using a CRT to measure amplitude and frequency of voltages.