1. Intensity I (W m-2)m-2)

2. Intensity = Power  I = P A Area

3. Inverse square law  I d 2 = A A  I d2d2 B B

4. Photoelectric effect frequency current fofo

5. Energy of photons E = h f h is Planck’s constant

6. Intensity of photons I = N h f N is number of photons per second

7. Work function Minimum energy to release electron from a surface (E = h fo)fo)

8. Kinetic Energy E = h f - h fofo Energy above minimum appears as kinetic

9. Emission spectra violet red W2W2 W1W1 W0W0

10. Emission spectra W2 W2 – W1 W1 = h f Electron ‘jumps’ from excited level to lower level

11. Emission spectra Bright emission lines - more electrons

12. Absorption spectra Photon of energy h f W2W2 W1W1

13. Absorption spectra W2 W2 = W1 W1 + h f Electron absorbs radiation and ‘jumps’ to excited level

14. Spontaneous emission random process

15. Stimulated emission Photon (energy h f)f) can cause atom to emit photon (energy h f) in phase and same direction

16. Laser Stimulating photon (hf) E1E1 E0E0

17. Laser Monochromatic Coherent Intense

18. Semiconductors n-type p-type

19. n-type Conduction by negative electrons

20. p-type Conduction by ‘positive’ holes

21. Forward-biased p-type diode conducts n-type electrons

22. Reverse-biased p-type diode does not conduct n-type

23. Diode Forward-biased diode electron and hole recombine Photon (heat) emitted

24. LED Forward-biased diode electron and hole recombine Photon (light) emitted

25. photodiode Photovoltaic mode supplies power e.g. solar cell

26. photodiode Photoconductive mode (reverse bias) light sensor

27. MOSFET drain n-region implant n-channel enhancement MOSFET oxide layer gate source n-channel p-type substrate

28. MOSFET Can switch on a load. Apply gate voltage V GS to turn ‘on’ MOSFET

29. D load n-channel enhancement MOSFET G S IoIo 0 V + V V GS

30. MOSFET Can also be used as an AMPLIFIER