Electric Current 19-1 page 694

Current and charge movement Electricity did not become an integral part of our lives until scientists learned how to control the movement of electric charge. –This is called current –Powers our lights, radios, T.V. sets, air conditioners, refrigerators –Also ignites the gasoline in car engines –Travels through computer chips –So many other devices …

Current is in your body! Connection between physics and biology Discovered by Luigi Galvani ( ) –Used electric sparks to cause a dissected frogs’ legs to twitch –Today, we know electric currents transmits messages between body muscles and brain

Current Current is the rate of charge movement –Suppose positive charges are moving through a wire –The current is the rate at which these charges move through the wire –See figure 19-1 in your text (page 694)

Equation and Variables Electric Current ∆Q = amount of charge passing through a given area ∆t = time interval I = current I = ∆Q / ∆t Electric current = charge passing through a given area time

Units! The unit for electric current (I) is the ampere (A)

Practice Question The current in a light bulb is A. How long does it take for a total charge of 1.67 C to pass a point in the wire?

Answer Given: –∆Q = 1.67 C –I = A Unknown = ∆t 2.00 seconds

Practice Question The compressor on an air conditioner draws 40.0 A when it starts up. If the start time is 0.50 seconds, how much charge passes a cross-sectional area of the circuit in this time?

Answer 20 C

Practice Question If the current in a wire of a CD player is 5.00 mA, how long would it take for 2.00 C of charge to pass a point in this wire?

Answer 400 seconds

Sources of current Batteries –Convert chemical energy to electric energy Generators –Convert mechanical energy to electric energy Such as plugging an electric device into an outlet Average potential difference is 120 volts

Current can be alternating or direct Direct current (DC) –Charges move in only one direction –Batteries always provide DC Alternating current (AC) –Charges move in forward and backwards directions –The power in your home is AC