Thermionic emission is the emission of free electrons from a heated metal surface. (p.175)
Cathode rays are high-velocity electron beams in a vacuum tube, attracted from the cathode to the anode by the E.H.T. supply. (p.175)
Cathode rays travel in straight lines, are deflected by electric fields towards the positive plate (negatively charged), and are deflected by magnetic fields (Fleming's left-hand rule). (p.178)
Cathode rays cast shadows and cause fluorescence, so they carry momentum and kinetic energy. (p.178)
Electrical potential energy eV = maximum kinetic energy ½mv2max. (p.179)
e = 1.6 × 10−19 C; m = 9.11 × 10−31 kg. (p.179)
5.2 Semiconductor Diode
A semiconductor diode allows current in one direction only (p-n junction). (p.182)
Forward biased: thin depletion layer, low resistance, current flows. Reverse biased: thick depletion layer, high resistance, no current. (p.182)
Rectification converts alternating current to direct current. (p.183)
Half-wave rectification: one diode passes only the positive half cycle. (p.184)
Full-wave rectification: a bridge rectifier of four diodes passes both half cycles in the same direction through the load. (p.184)
A capacitor in parallel with the load smooths the output by charging as voltage rises and discharging as it falls. (p.186)
5.3 Transistor
A transistor has three terminals: emitter (E), base (B), collector (C); types are npn and pnp. (p.187)
A small base current IB controls a large collector current IC; the large base resistor limits IB. (p.188)
Current amplifier: amplification factor β = IC/IB = gradient of the IC–IB graph; IE = IB + IC. (p.190)