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Published byMargery Logan Modified over 9 years ago
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Electric Current
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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)
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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
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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
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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
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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?
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Color Code Resistors have four color bands setting its value. 1st 2nd × 10 3rd ± tolerance Ex. What is the value of the resistor?
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Power Power is energy used per time. How much power is used by a 0.89 resistor when 25 volts is applied over it?
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Defibrillator From the diagram can the current, voltage, resistance and power be calculated?
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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
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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
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