johann wilhelm hittorf discovered that electrons have a negative charge.
johann wilhelm hittorf discovered that electrons have a negative charge.
who discovered that electrons have a negative charge?
johann wilhelm hittorf
Na
Na
a sharply focused beam of electrons (a cathode ray) is generated by the electron gun at ground potential and accelerated by the anode (the first dynode of the electron multiplier) around the gun at a high positive voltage (approx. +1500 v). once it exits the electron gun, its inertia makes the beam move away from the dynode towards the back side of the target. at this point the electrons lose speed and get deflected by the horizontal and vertical deflection coils, effectively scanning the target. thanks to the axial magnetic field of the focusing coil, this deflection is not in a straight line, thus when the electrons reach the target they do so perpendicularly avoiding a sideways component. the target is nearly at ground potential with a small positive charge, thus when the electrons reach the target at low speed they are absorbed without ejecting more electrons. this adds negative charge to the positive charge until the region being scanned reaches some threshold negative charge, at which point the scanning electrons are reflected by the negative potential rather than absorbed (in this process the target recovers the electrons needed for the next scan). these reflected electrons return down the cathode ray tube toward the first dynode of the electron multiplier surrounding the electron gun which is at high potential. the number of reflected electrons is a linear measure of the target's original positive charge, which, in turn, is a measure of brightness.
video camera tube