1. Electric Current

2. Current Rate at which charge flows through a surface. Ex. If the charge on a capacitor changes by the function Q(t)=6(1-e  0.1t ), what is the charge on the capacitor and current leaving the capacitor at t = 5s? Units - Ampere (A)

3. Drift Velocity Factors that affect current flow n depends on density of material and number of free electrons/atom. In a typical conductor drift velocity is ~0.25 mm/s. How does electrical devices respond so quickly? n – carriers/volume q – charge/carrier A·v d = A  L/  t– volume/time

4. Ohm’s Law Current Density is the amount of current per unit area. Ohm’s Law - The ratio of current density and electric field are constant.  - conductivity 250  12 V I BatteryResistor e-e- e-e- e-e- e-e- e-e- e-e- A

5. Resistance The common form of Ohm’s law is Resistance must then be related to length, area, and conductivity. Units - Ohm’s (  )  - resistivity Temperature Dependence T 0 = 20 °C

6. Resistors Ex. What is the resistance of a cylindrical rod of carbon that is 2.0 cm long and has a radius of 0.50 mm? If 25 volts is applied across this resistor, how much current will flow? What is the resistance at 40 °C?

7. Color Code Resistors have four color bands setting its value. 1st 2nd × 10 3rd ± tolerance Ex. What is the value of the resistor?

8. Power Power is energy used per time. How much power is used by a 0.89  resistor when 25 volts is applied over it?

9. Defibrillator From the diagram can the current, voltage, resistance and power be calculated?

10. Semiconductors Silicon and Germanium have 4 valence electrons and form 4 covalent bonds with its neighbors giving a neutral crystal structure. Doping – Using atoms with a valence of 3 or 5 give a deficit or surplus of electrons in the crystal structure. Si P B N-type (extra e - )P-type (missing e - )Un-doped  =23  m  <0.1  m

11. PN Junctions Near the junction excess e- from N-type diffuse to places of missing e- in P-type semiconductors. P-typeN-type P-typeN-type Depletion Zone P-typeN-type Depletion Zone P-typeN-type Diode E field