Electric Current Chapter 34

Flow of Charge Heat Flow Heat flows from higher temperature end to lower temperature end Heat flow ceases when both ends reach the same temperature

Flow of Charge Charge Flow Charge flows from one end to another when there is a potential difference When there is no potential difference, there is no longer a flow of charge

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) Given : 15 amps = How many electrons each second?

Electric Resistance 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)

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

Ohm’s Law I = V/R What happens to current, when the voltage is doubled? What happens to current, when the resistance is doubled? How much current is drawn by a lamp that has a resistance of 100 ohms with 50 V?

Conducting Circuit Material Source of Electrons Conducting Circuit Material electrons do not come from voltage source; voltage source provides the energy electrons vibrate to and from fixed positions

Electric Power = (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 of a 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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