Electric Current Chapter 17

Capacitance Ability to store charge Capacitance = Charge/Potential Difference C = Q/V

Parallel Plate Capacitors Capacitance = permittivity * Area/Distance C = ε0A/d

Flow of Charge Heat flows from higher temp to lower temp as long as temp difference Water flows from high to low potential

Flow of Charge Charge Flow Charge flows when there is a potential difference When there is no potential difference, there is no longer a flow of charge

An electric “pump” is needed for potential difference Voltage Sources An electric “pump” is needed for potential difference The potential energy per coulomb of charge is the voltage Voltage is the “electric pressure” to move e- between terminals

Voltage Sources (con’t.) Generators convert mechanical energy to electrical energy example: alternator in automobiles Wet/Dry Cells energy released in a chemical reaction is converted to electrical energy

Electric Current Unit for Charge Coulomb = the charge of 6.25 X 1018 electrons

Electric Current Current - I Flow of charge Unit: ampere (amp) Flow of one coulomb of charge per second Unit: ampere (amp)

Electric Resistance…is futile Resistance - R Resistance to flow Unit: ohm () Dependent on material used in wire, temperature (greater in higher), length (less in shorter), and thickness (less in thick)

Potential Difference (voltage) - V Electric Potential Potential Difference (voltage) - V Electric Potential Energy / Charge Unit: Volts (V)

Ohm’s Law I = V/R V = IR Bicycle analogy No new chain created

Electric Power P = I V 1 Watt = (1 amp) (1 volt) 1 kilowatt = 1000 watts 1 kilowatt - hour = amt. Of energy consumed in 1 hour at the rate of 1 kilowatt

Practice Problems If a circuit has a resistance of 40 ohms and a current of 3 amperes, what is the voltage across the circuit? A radio that has 360 ohms of resistance is plugged into a typical 120 volt wall outlet. What is the current in the radio?

Practice Problems 2 What is the wattage in the bulb in a lamp (on 120 V outlet) that draws .833 amperes? If you use an average of 550 watts of power in the lights in your house, and they are on an average of 16 hours a day, what is your energy usage for a 30 day month?

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