4. Semiconductor Thermistor at T = 0K Full of electrons Full of holes (free space for electrons) Thermistor above absolute zero energy At the hotter temperature electrons can get into the conducting band
5. Superconductors Some special material can become superconductors The superconductor has to be cooled down to its critical temperature (Tc) At the critical temperature the resistance fall to zero These can be used to make low loss power lines and very good electromagnets Resistance Temperature (k) 0 Tc The world record Tc of 138 K
6. String the resistance resistor V I bulb V I Diode V I 0.7 Make sure you get the right axis V =IR
12. Calculate the resistances and then measure them in real circuits to prove it R1 R2 R3 What happens to the total resistance in the parallel circuit? R1 R2 R3
13. Quick questions Calculate the resistance of these circuits 4 Ω 12 Ω 4 Ω 12 Ω 2 Ω 6 Ω 3 Ω Rt =R1 + R2 +R3
14. Answers Calculate the resistance of these circuits 4 Ω 12 Ω 4 Ω 12 Ω 2 Ω 6 Ω 3 Ω 4 + 12 = 16 Ω 1/R = 1/12 + ¼ R = 3 Ω Parallel part first 1/R = 1/3 + 1/6 R = 2 Plus the 2 ohms in series R = 2 + 2 R = 4 Ω
15. Another question (because I could not fit it on the last slide!) 9 Ω 4 Ω 2 Ω 3V 1)Calculate the total resistance of the circuit 2)The battery current 3)The power supplied from the battery 4) The power supplied to the 9 ohm resistor P = I 2 R V = IR P = IV P = V 2 /R
16.
17. Flow of current The same number of electrons will flow in as they flow out A A Measure the current, to discover how the electrons flow through each line A R1 R2 R3
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