1. 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

2. 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

3. 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
Q Q2
r1,2

4. 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.
Q Q Q3
r1, r2,3
r1,3
Systems of more charges requires terms

5. 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

6. The Work Done to Disassemble a Hydrogen Atom
(-) r = .529 x 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 = eV. This is, in fact, the ionization energy of hydrogen

7. 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

8. 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

9. 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.