Cathode Ray tubes allow a manipulation of a stream of charged particles
*CRT - consist of evacuated glass tube containing two electrodes
*High voltage is applied across electrodes - stream of negatively charged particles from cathode to anode
*Structures built around the cathode (e.g. electric plates and magnetic coils) can be used to manipulate CR
Charge particles produce an electric field
*Electric field exists in any region that an electrically charged object experiences a force
*A charge in an electric field experiences a force F = Eq
Oppositely charged parallel plates
*Electric field moves uniformly from positive to negative
*For oppositely charged plates - E = V/d
Force acting on a charge moving through a magnetic field
*Charges moving through a magnetic field produces a force
*F = qvbSin+
*Force greatest when particle is perpendicular to electrical field
Thompson's experiment to measure charge/Mass ratio
*Subjected cathode ray to deflection by know electric and magnetic fields - set at right angles to each other
*Arranged magnetic and electrical forces to balance out forces acting out of CR
*-ve particles from cathode move through a collimating anode - subject CR into thin beam
*A known magnetic field was applied, and the electrical field, once applied, was adjusted to until returned to O
Fb = Fe
qvB = qE
v = E/B - which finds velocity of particle
Then
Fb = Fc
qvb = mv2/r
q/m = V/Br
Outline role of Cathode ray in
*Electron gun
oConsists of
"XA thermionic cathode - ejects electrodes when heated
"XA anode - collimator to subject beam to a thin stream
"XGrids to control brightness
*Electric field or deflection system
oHelps to deflect CR for various uses
oConsists of two parallel plates - one horizontal the other vertical
*Fluorescent screen
oEnd of the CRT coated with fluorescent...
Illustration showing the interior of a cathode-ray...
A close-up on a CRT screen
English: The Crookes tube with which JJ Thomson de...