Electric Current, ( I ), is the flow of electric charge. More specifically, it is defined as the _____ at which charge flows. Units: ____________, which is defined as 1 _______ (____ for short), with the symbol ___ (1 ___ = 1 ___ = 6.25x10 18 ___) rate Coulombs/sec Ampere Amp A AC/se - /s Electrical Current (I)

Current in AmpsEffect on human body (1 mA)Can be felt (5 mA)Painful (10 mA)Involuntary Muscle Spasms (15 mA)Loss of Muscle Control (70 mA) If through heart, serious disruption; probably fatal if > 1 second ( mA) Uncontrolled “twitching” of heart > 0.2 (> 200 mA) Heart stops, but may be able to be revived easier than 0.1 – 0.2 A Current’s Effect on the Human Body…

Some Interesting Currents… Defibrillator 35 A!! Police Taser 162 mA

But in order to sustain a current, the difference in potential (or voltage) must somehow be maintained. The situation is analogous to the flow of water… The flow will continue until the water levels are ____ _____ and at that point there is ____ pressure difference. Pictures from Hewitt’s Conceptual Physics Current: Cause and Effect _______ is the cause, and _______ is the effect. Voltagecurrent the same NO

A “voltage source” (such as a battery or generator) performs a similar function as this water pump…. It maintains an electric potential difference so that a current can be sustained. A voltage source, then, is like an electrical pump, and voltage can be thought of as _________ _________. The pressure difference could be maintained by adding a ______. pump electric pressure

There are two common types of voltage sources : There are two Types of batteries: ____cells such as AAA, AA, C & D (all 1.5 Volts) 6 volts, 9 Volt, etc. ____ cells such as a 12 V car battery Examples of Voltage Sources batteries and Dry Wet generators

So, a 1.5 V battery has a 1.5 V potential difference between the (+) and (-) terminals. When connected to a small light bulb via wires, that difference “pushes” __________ through the circuit, from the ( ) terminal to the ( ) terminal, supplying 1.5 _______ of energy per coulomb of charge that flows through the circuit. Note: Because of historical precedent, the current direction in textbooks is still drawn in the direction in which positive charge carriers would move. + - e-e- I electrons - + Joules

Applications 1. How can birds perch or squirrels run along high voltage wires (1000’s of volts) and not be fried?? To receive a current (shock) there must be a __________ in potential between one foot and the other. IF they landed with one foot on one wire and the other foot on a neighboring wire at a different voltage, then ___________ difference ZAP!!!!

2. A “hot wire” is one that is NOT electrically neutral. If, while attempting to fix a light fixture, you touch a 120 Volt “hot wire” with one hand while touching a neutral or ground wire with the other hand, ____________________________. 3. Testing whether a wire is “hot” by touching it: If you were to touch a “hot wire” with your hand, the current could stimulate the muscles in your hand to contract, causing your hand to close and clamp around the wire (BUMMER!) Instead, touch the hot wire with the _____ of your hand (or better yet, use a meter or call an electrician!) ZAP!...current through body back “Hot” Wires

Electrical Resistance, (R) While voltage causes current, the amount of current produced also depends on the electrical resistance (electrical “________”) that the conductor offers to the flow of charge. The components of a circuit (such as a light bulb filament, an electrical device called a “resistor”, a motor, etc.), as well as the _____ in a circuit have electrical resistance. Color-coded Resistors The resistance depends fundamentally on the material’s “conductivity” (how good of a conductor the material is.) friction wires

Back to our water analogy… For a given pressure, more water will pass through a ______ pipe than a ______ one. We could say the ______ pipe, then, offers more “resistance”. The resistance of a wire depends on three things: The __________ of the wire The ________ of the wire The _______ of the wire conductivity thickness length thickerthinner

In the same way, for a given voltage, more electric current would pass through a _______ wire than a _______ one. The _______ wire offers more resistance. And logically, a ______ pipe would offer more resistance to the flow of water than a _______ pipe. ( Select shorter or longer.) In the same way, the ______ a wire is, the greater the resistance. ( shorter or longer ) thickerthinner longer shorter longer Example: Wire ___ has the most resistance and Wire ___ has the least resistance. (a, b or c) b a L