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 (1737-1798)– 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 intervalI = 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 0.835 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 = 0.835 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