1. Circuit Electricity May 30, 2012 Chapter 22

2. Terms  Current: Flow of charge  Symbolized by “ I ”  Units = Coulombs/second = Amperes (A)  Circuit: a closed loop that current flows through  Resistance: Opposition to current  Units = Ohms ( Ω )  LED: Light Emitting Diode  Used to test for presence of current.

3. More Terms  Volts: the force that pushes current through a circuit  Power: the energy delivered to the circuit per second  Power = (current)(voltage)  P = ( I )(V)  Units = Watts

4. Examples #1 & #2  A car battery causes a current of 2.0 amps through a light while 12 V is across the battery. What is the power used by the lamp?  P = (2.0)(12)  P = 24 W  What is the current through a 75W lightbulb connected to a 120 V outlet?  75 = ( I )(120)  I =.625 A

5. How does a light bulb light?  As the current flows through the filament, it encounters resistance  Resistance: a material’s opposition to current flow  Ohm’s Law:  R = (V/ I )  As resistance increases, current decreases  As voltage increases, current increases  The collisions between the current and material results in energy loss (heat and light)

6. Examples #3 & #4  A car headlight has a resistance of 30 Ω and is hooked to a 12V battery. What is the current through the bulb?  30 = (12/ I )  I = (12/30) =.40 A  A lamp draws a current of.50A when connected to a 120-V outlet. What is the resistance of the lamp?  R = (120/.50)  R = 240 Ω

7. Homework  Ch 22  p 527-529  # 22,23,25,27,30,33,42,45