2. By a Gentleman

3.  All conduction is due to the movement of free electrons. + - I’m free In a Semiconductor the electrons are fixed until they receive a little energy

4.  Conduction half way between a conductor and an insulator  Crystals of Silica A photon releases an electron that now can carry current I’m free

5.  These contain doping with atoms of different valency Doping is adding a material of a different valency to increase the conductivity.

6. Thermistor Digital thermometer 10°C Water Heat source Ω Glycerol

7.  Near the junction some electrons from the ‘N’ fill the holes in the ‘P’ crystal. N-typeP-type

8.  This creates area in the middle where there are no carriers so no conduction P-typeN-type This barrier is called the DEPLETION LAYER

9.  When the diode is in FORWARD BIAS the depletion layer disappears. The diode conducts. P-typeN-type + -

10.  When the diode is in REVERSE BIAS the depletion layer increases. The diode acts as a barrier or insulator. P- type N- type - +

11.  Only allows current in one direction Forward BiasReverse Bias

12. V/ v I/ A Junction Emf (0.6V) Must be Overcome before Conduction starts In reverse Bias No conduction

13. mA V + 6 V - Diode in forward bias

14. Diode in Reverse bias V + 6 V - A A

15.  Uses this to turn AC to DC This is called half wave rectification Mains Resistor

16.  We use a capacitor to smooth the signal to get something more like DC

17.  Electrons leaving the surface of a hot metal Hot Metal e-e- e-e- e-e- e-e- e-e-

18.  First we heat the cathode to make the electrons jump off by Thermionic Emission CATHODECATHODE e-e- e-e- We can use a voltage to accelerate the electrons to form a stream ANODEANODE High Voltage

19.  We calculate the energy of each electron first in electron volts CATHODECATHODE e-e- e-e- Energy Gained = 2000eV ANODEANODE 2000v

20.  Then we convert this to joules ( Charge on the electron = e = 1.6x10 -19 C) CATHODECATHODE e-e- e-e- Energy Gained = e.V = 1.6x10 -19. 2000 = 3.2x10 -16 Joules ANODEANODE 2000v

21.  All the energy on an electron must be kinetic energy. CATHODECATHODE e-e- e-e- Energy Gained = 3.2x10 -16 = 0.5mv 2 ANODEANODE 2000v

22.  Electrons jump from the surface of a hot metal –  Thermionic Emission Accelerated by high voltage they smash into tungsten Most of the electron energy is lost as heat.-about 90% X-rays very penetrating, fog film, not effected by fields. High Tension Voltage