Notes

Electric Current
-Current + voltage difference (underlined)
-electric current - the net movement of electric charges in a single direction
-electric current is measured in amperes (A)
-1 ampere = 1 coulomb of electric charge flowing past a point every second
-if electrons are in constant movement in all directions, there is no net movement of electrons in 1 direction
-when there is an electric current in a wire, then the electrons' random movements drift in the direction of the current
-in the same way water flows from higher pressure to lower pressure,
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-electric current is from higher voltage to lower voltage
/- - - - - --> / -
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- - - -- / /
-voltage difference - related to the force that causes electric charges to flow
-measured in volts (V)
-electric circuit - a closed path that electric current follows
-there is no current once something is disconnected
-the flow of electrons + the current are in opposite directions:
-the direction of the electric current is always from higher voltage to lower voltage
-the electrons in a circuit actually flow from the lower voltage to higher voltage
-Batteries (underlined)
-batteries are power supplies
-dry-cell batteries - cylindrical batteries that are placed in flashlights
-a cell consists of 2 electrodes surrounded by a material called an electrolyte
-electrolyte - enables charges to move from 1 electrode to the other
-wet-celled battery - contains 2 connected plates made of different metals or metallic compounds in an electrolyte
-the electrolyte in a wet cell is conducting a liquid solution
-most common type of wet-cell battery in use today is a car battery
-lead-acid battery - contains a series of 6 wet cells composed of lead + lead dioxide plates in a sulfuric acid solution
-the chemical reaction in each cell provides a voltage difference of about 2 V, giving a total voltage difference of 12 V
-a voltage difference is also provided at electrical outlets, such as a wall socket
-electrical outlet voltage difference is usually higher than the voltage difference provided by batteries
-in the US, the average voltage difference across the 2 holes in a wall socket is usually 120 V
-Resistance (underlined)
-resistors - designed to resist the flow of electrons
-help protect more delicate electronic components from melting or breaking if too much current is sent through them
-when electrons move through a resistor, some energy is transferred to that resistor
-resistance, measured in ohms (Ω) - the tendency for a material to resist the flow of electrons + to convert electrical energy into other forms of energy, such as thermal energy
-why cell phones get hot during a long phone call
-almost all materials have some resistance (even copper wires)
-Ohm's law (underlined)
-the relationship between voltage difference, current, + resistance in a circuit is known as Ohm's law:
current (amperes A) = voltage difference (volts V) / resistance (ohms Ω)
I=V/R
-Ohm's law - the current in a circuit equals the voltage difference divided by the resistance
-Alternating current + direct current (underlined)
-the AC in AC/DC stands for alternating current
-in the US, electric power grids are built so that alternating current changes direction 120 times each second (that's why you never notice the blinking of lightbulbs)
-the DC in AC/DC stands for direct current
-battery-powered devices, such as flashlights, use direct current
-direct current never changes direction (unlike alternating current)
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