19-1 Electric Current
Luigi Galvani (1737-1798) discovered that electric
currents are part of human physiology.
Current is the rate of charge movement (measured in
amperes).
I = Q/t
Conventional current is defined as positive charge
movement.
Ion a charged atom
Electrolyte a solute that consists of charge carriers;
it can conduct electricity to a degree
Drift velocity is the net velocity of charge carriers;
its magnitude is much less than the average speed between collisions.
Batteries convert chemical energy to electrical energy.
Generators convert mechanical energy to electrical
energy.
Direct current (DC) charges move in a single direction
Alternating current (AC) the direction of the charge
constantly alternates
19-2 Resistance
Ohms Law - Potential difference equals current times
resistance
Potential difference = voltage (measured in volts)
V=IR
Resistance is measured in ohms.
Resistance depends on length, cross-sectional area,
temperature, and material.
More resistance longer,
smaller cross-section, hotter
Less resistance shorter,
larger cross-section, colder
Resistors can be used to control the amount of current
in a conductor.
Salt water and sweat lower the bodys resistance.
Ohms Law doesnt work for all materials.
Superconductors are materials that have resistances
of zero when the temperature is below the critical level for that material.
19-3 Electric Power
Electric power is the rate of conversion of electrical
energy.
P=IV
P=I2R
P=V2/R
Electric companies measure energy consumption in kilowatt-hours.
Electrical energy is transferred at high potential
differences to minimize energy loss. |
