![]() ![]() This is shorter than the time that the brain retains each image so that the screen does not seem to flicker. Each scan takes one-fiftieth of a second. The odd-numbered lines are drawn first, then the beam 'flies' back to the start and draws in the even-numbered line. Beams are switched on and off at the appropriate spots on the screen in order to reproduce the transmitted picture -Each picture is formed from two passes of the electron beam. The picture on the screen is formed by scanning the beam from left to right and top to bottom. The magnitude and direction of the current determine the degree and direction of electron beam deflection. Magnetic field coils placed outside the tube produce horizontal and vertical magnetic fields inside it. information is transmitted to the receiver, which signals the electron guns. Dots of red, blue, green phosphorescent paint on the screen convert the energy of the electron beam into coloured light -Each gun only strikes its respectively coloured phosphor dots -Different colours are formed by combinations of red, blue, green dots grouped very close together. Coloured television uses three electron guns, corresponding to primary colours red, blue, green. These are being replaced by LCD and plasma screens. conventional television displays use cathode ray tubes. Hence Thomson could calculate charge to mass ratio q/m F_c=F_M (mv^2)/r=qvB q/m=v/rB v was found from earlier, r measured, B is known. Magnetic force provides centripetal force, rays bend in a circular arc. He then applied the same strength magnetic field alone. For magnetic field number of turns and current of electromagnet known). F_E=F_M qE=qvB v=E/B E and B were known (for electric field E=V/d and V and d known. ![]() Equated electric and magnetic force equations to determine velocity of cathode ray particles. *diagram SuccessOne Physics Thomson varied the fields until their opposing forces cancelled, leaving the cathode rays undeflected. The fields were arranged at right angles to each other, producing forces on the cathode rays that directly opposed each other. He built a cathode ray tube with charged parallel plates to provide a uniform electric field and electromagnets outside the tube to provide a uniform magnetic field. ![]() Thomson aimed to prove that cathode rays were a stream of negatively charged particles by determining the charge to mass ratio of these particles. *note: Maltese cross experiment shows that cathode rays travel in straight lines which seems to work for either particle or wave. (current too small and equipment not sensitive enough) -Hertz found that the rays were not deflected by an electric field and concluded they had no charge (his experiment was faulty, gas pressure in tube was too high) Thomson's electric plate experiment was taken as conclusive evidence that cathode rays are negatively charged particles. The atomic structure wasn't yet known.) -It was known that moving charges produce a magnetic field, but o magnetic field could be detected around the rays. (because the space between atoms is much larger than an electron. Implied the rays carry momentum which they imparted to paddlewheel (unknown by Crookes at the time, this is actually due to the radiometric effect and has nothing to do with momentum) Wave -Can pass through thin gold foil without damaging it. Scientists disagreed over whether cathode rays were beams of negatively charged subatomic particles or electromagnetic radiation because they seemed to show characteristics of both waves and particles Particle -deflected by magnetic fields in the same way as negatively charged particles -deflected by electric fields in the same way as negatively charged particles (repelled by negative plate and attracted to positive) -small paddlewheel turned when placed in their path. ![]()
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