ELECTRON DYNAMICS AND CRO

Intoduction:-

Charged particles:-The electronic devices operate through the motion of the charged particles,usually electrons under electric and magnetic field.The study of trajectories of projectiles usually electrons under the influence of electric and magnetic fields is called as electron ballistics or electron dynamics.

The charge of an electron is 1.6*10^-19 C (where Couloumb (C) is the unit of charge).

Mass of an electron:-The electron poesses a definite mass.A Direct measurment of teh mass of electron cannot be done.The e/m ratio i.e charge/mass ratio is determined by conducting number of experiments as 1.759*10^11C /kg.By knowing e/m value mass of an electron is determined as 9.107*10^-31 kg.

Key point:The radius of an electron is approximately equal to 10^-15 m and that of an atom is 10^-10 m.

Electric field intensity(E):-It is defined as the force on a unit positive charge at any point in an electric field.It's formula is E=V/d volt/metre,where V=Potential in volts,d=distance in metres.

Force on a charged particle in an constant electric field:-

• The force acting on a charge 'q' in an electric field intensity (E) is given by F=Eq.
• But in general to calculate the path of charged particle in an electric field ,the force is related in terms of mass and acceleration of the particle,according to newton's second law we have F=ma=m*dv/dt where (a=dv/dt).
• Thus on equating we get,Eq=ma,therefore a=Eq/m.
• If the electric field is constant and towards the -ve X-direction and the movement of electron is in +ve X-direction,and the electric field components along Y and Z direction are zero,then the above equation changes as a(x)=Eq/m=constant.
• On integrating we get the velocity of the electron in X-direction,v(x)=Eq/m+v(ox) where v(ox) is the intial velocity of electron.
• On further integration we get,the displacement of the particle as x=a(x)t*t/2+v(ox)t+x(o).
• Here x(o) is the intial positon of the electron.
• However,when E is a time varying function ,the above equations are not applicable ,then the equation a(x)=Eq/m,should be integrated where E is time varying and a(x)=dv(x)/dt ,v(x)=dx/dt.