72 chatode ray consist of negative charged particle. The negative particle is called
electron by Thomson. According to the opinion of Thomson, electron is much lighter than atom, and electron is found in all material. It means atom is not the
smallest part of matter. It gives a motivation for Thomson to propose the atomic model to repaire the atomic model of Dalton.
Figure 9.2. William Crookes
Based on the experiment which have been conducted, it is found some characteristic of chatode ray as follow:
o Propogate in straight line.
o It can cause zinc sulfide and barium platinasianide fluoresence
o It consists of negative charged particles electron
o It can produce heat
o It can be black of photograph film
o It deflects in magnetic field
o It deflects in electric filed
o It can produce x-ray
Pada saat ini tabung sinar katoda dimanfaatkan untuk tabung televisi, tabung CRO, tabung sinar x, dan monitor computer.
B. Lorentz Force
Each charge particle positive ion, negative ion, electron, etc Which placed in magnetic field will get force which is called Lorentz force. The difection of
this force is according to Lorentz rule leff handed rule, if main finger shows the direction of magnetic field B, middle finger shows the motion of positive
particle, then thumb shows the direction of Lorentz force.
73 Figure 9.3. Left Handed Rule Lorentz Rule
Lorentz force which is undergone by the charge particle which move with velocity of v in magnetic fielf of B is:
B x
v q
F
L
9.1 The magnitude of Lorentz force which is undergone by charge particle is:
sin qvB
F
L
9.2 where q is the charge of particle, and
angle between velocity vector and magnetic field.
If the charge particle move perpendicular with the direction of magnetic field, then the particle will move in circular path. In that charge particle exerts
two kind of force Lorentz force and sentripetal force. In this condition, the equilibrium force is occurred:
Figure 9.4. Circular path of Electron Orbit in Magnetic Field
qB mv
R R
v m
qvB F
F
sv L
2
2
9.3
Where R radius of circular path of charge particle, m mass of particle, and q charge of particle.
74
C. Motion of Charged Particle in Electric Field E
The charge particle q moves in electric field E will be effected by electric field then path of particle undergoes deflection. Magnitude of electric force or
Coulomb force which exerts in particle can be written: qE
F
C
9.4
A positive charged particle in electric field will be deflect in far away tron the direction of incident electric field. On the other hand, a negative charged
particle will be deflect close to the direction of incident electric field.
Figure 9.5. Motion of Charged Particle in Electric Field E If charged particle move in electric field and magnetic field simaultaneusly
then it will be several possibilities. One of the possibities the intensity of electric field and magnetic field is seted until the electric force and magnetic force have the
same effect in opposite direction then the particle move in straight line. Jika muatan yang bergerak adalah elektron maka berlaku persamaan:
evB eE
F F
L C
9.5
where
d V
E
9.6 Subtitute equation 9.6 in 9.5 is obtained:
Bd V
v
9.7 Where v : velocity of electron
V: potential difference between both electrode d : distance between both electrode
B: intensity of magnetic field F
E
-
+ +q
v v
75
D. Thomson Experiment of Cathode Ray
