Electric+Currents

__Difference between Voltage and Currents__ __Electric Resistance__ Resistance __Health Effects__ __Direct Current versus Alternating Current__ __AC/DC__ >>> When a battery or generator is connected to the wire and electric field is established inside the wire, nudging >>> Energy is carried by the electirc field and causes a vibratory motion of the electrons that already exist
 * __Electric Currents__**
 * While heat will flow through a conductor from an area of high concentration to an area of low concentration, until both areas are the same temp
 * When the ends of an electric conductor are at different electric potentials, charge flows from one end to the other
 * Charge flows when there is a __**POTENTIAL DIFFERENCE**__
 * When potential, (voltage) is different from one end to the other, there will be a flow of charge, until there is no longer a difference
 * **Electric Current** - is the flow of electric charge
 * In solid conductors, like metals, the charge is carried by the freely moving electrons, which are not bound to the nuclei
 * In fluid conductors, like electrolytes in car batteries, not only the electrons, but also the positive and negative ions will carry the charge
 * **Electric Current** - is measured in __**AMPERES**__
 * 1 Ampere is the flow of 1 Coulomb of charge per second
 * **Net Charge on a wire** - while the current is flowing, electrons flow through the network composed of positively charged atomic nuclei
 * The number of electrons entering the wire is equal to the number exiting the wire at the other end, giving the wire a net electric charge of __**ZERO**__
 * **Voltage Sources** - charge will not flow unless there is a difference in potential, to sustain a current flow, there must be a kind of "pump" to keep the difference from reaching zero
 * Batteries and Generators are capable of sustaining differences in potential
 * In batteries, chemical reactions occurring inside releases electrical energy
 * In generators, like the alternator in a car, mechanical energy is converted to electrical energy
 * Power companies use electric generators to provide the 120 volts delivered to home outlets
 * The alternating potential difference between the two holes in the outlet averages 120 volts
 * The alternating potential diffrence between the two holes in the outlet average 120 Volts
 * When the prongs of a plug are inserted into the outlet, an average electric "pressure" is placed across the circuit connected to the prongs
 * As an analogy, consider a long pipe filled with water
 * water will flow through the pipe if there is a difference between the ends of the pipe, water flows from the high pressure end to the low pressure end, only the water flows, not the pressure
 * across a wire, the current is like water, it it flows through the wire, based on the voltage differences (pressure diffrences)
 * the amount of charge that flows in a circuit depends on the voltage provided by the source
 * the current also depends on the resistance that the conductor offers to the flow of charge - the electric resistance
 * The resistance of the wire depends on the conductivity of the material used in the wire (how well the wire conducts) and also on the thickness and length of the wire
 * the resistance of a wire depends on the conductivity of the material used in the wire and also on the thickness and length of the wire
 * Long Wire = more resistance, farther for charge to travel
 * Short Wire = less resistance, less distance to travel
 * Thick Wire = less resistance, more potential area for charge to use, like more lanes of traffic
 * Thin Wire = more resistance, like a single lane of traffic
 * For most conductors, higher temperatures = higher resistance
 * some materials experience zero resistance at very low temperatures, a phenomenon known as __**SUPERCONDUCTIVITY**__
 * certain metals acquire this at temps near absolute zero
 * can be found in a variety of nonmetallic compounds at very high temperatures
 * once electrons current is established in a superconductor, the electrons flow indefinitely
 * electric resistance is measured in __**OHMS**__, named after Georg Simon Ohm
 * OHM's Law states: the current in a circuit is directly proportional to the voltage impressed across the circuit, and is inversely proportional to the resistance of the circuit
 * in a circuit, if voltage is increased, current is increased; if resistance is increased, current decreases
 * The resistance in a typical lamp cord is much less than 1 ohm, while the light bulb has a resistance of about 100 ohms. The resistance of an iron or electric toaster is about 15 - 20 ohms, allowing more of the voltage to flow and produce heat
 * In televisions or radios, the current is controlled by a series of elements called resistors, which range in ability from a few ohms to millions
 * What causes electric shock on the human body, current or voltage?
 * The damaging effects of electric shock are the result of __**CURRENT**__ passing through the body
 * The resistance that the body offers to a current depends on the conditions of the skin exposed
 * If the skin is soaked with salt water, the resistance is only about 100ohms, while if the skin is very dry it can provide resistance of 500,000ohms
 * Most fatalities involving electricity occur from common 120 volt electric circuit
 * If you touch a faulty fixture while standing on the ground, your shoes will provide a considerable resistance to the current
 * If you touch a faulty fixture while standing barefoot in a tub of water, which is connected to the ground through the plumbing, then your body provides very little resistance to the current and you might die
 * While distilled water is a good insulator, ordinary water contains ions that reduce the resistance of the water
 * There is usually a layer of salt on human skin left over from perspiration, which when wet lowers the resistance of the skin to a few hundred ohms or less
 * bottom line, handling electric devices while bathing is extremely dangerous
 * So why dont birds perched on power lines get electrocuted?
 * the body of the bird is at the same potential as the potential of the current flowing through the wire
 * unless there is a difference in potential, there will be no benefit for the current to flow through anything but the path of least resistance which is the power line
 * if you were to fall from a height and managed to catch a power line, as long as you didnt touch anything but the line, you would not receive a shock
 * if you were to reach out and touch another line of different potential, then the current would flow through you and you would fry
 * if you touch surfaces of different potentials, you become a pathway for current
 * to prevent mild shocks from happening when you touch surfaces of appliances are connected to a ground wire
 * the ground wire is connected to the 3rd prong of a three wire electric plug
 * all ground wires are connected together through the wiring system of a house/building
 * the 2 flat prongs are for carrying current
 * if the live wire accidentally comes in contact with the metal surface of an appliance, the current will be directed to the ground rather than to anyone who happens to touch it
 * one of he effects of electric shock is to overheat tissues in the body
 * another is to disrupt normal nerve function
 * another is to upset the nerve center that controls breathing
 * first thing to do to help electric shock victims is to clear them from the supply of power with a wooden stick or other nonconductive object
 * artificial respiration is the next step if required
 * electric current is either in AC or DC
 * DC or direct current is literally current that flows in one direction, always
 * batteries are direct current energy flows, as the terminals marked positive are always that, and vice versa
 * electrons always are moving from the repelling negative terminal, to the attracting positive terminal
 * AC- or alternating current- is current that does what the title suggests, it starts in one direction, then turns around and goes the opposite direction
 * The electricity in North America is AC and alternates at a frequency of 6o cycles per second, 60-herts current
 * Voltage in North America is primarily 120 volts
 * In the early days of electricity, high voltages burned out filaments of lightbulbs too easily, so a lower power supply was developed, at about 110 volts.
 * This became the standard, even when better bulbs could bo developed that could stand a higher voltage.
 * So the USA still has a system of 110 (120 is more accurate) volts, while Europe went with the 220 Volts
 * If we travel to Europe, we must be carfeul about our electric devices...
 * The current in a house is AC.
 * The current in a battery-operated device(laptp computer, cell phone, ect.) is DC
 * With an AC-DC converter, you can operate a batery- run device on AC instead of batteries.
 * Inside the converter is a transformer (not the Optimus Prime type) that lower the voltage.
 * Also inside is a diode, a tiny electronic to flow in only one direction.
 * That is not enough, as AC current vibrates in two directions.
 * In AC passing through a diode, the result would be only rough DC as only half the cycle would go trough.
 * To smooth the output, a capacitor is used to produce a retarding effect on charges in current flow.
 * The speed of electrons in circut
 * At room tempurature, the electrons inside a metal wire have an average speed of a few million km per hour due to their thermal motion.
 * This does not produce a current because the motion is random, no net flow in any one direction.
 * The sources of electrons in a circuit
 * The source of electrons in a circuit is the conducting material itself.
 * Outlets in homes are AC.
 * Electrons do not travel great distances through a wire in an AC circuit. Instead they vibrate to and from about relatively fixed postions.
 * When you plug a lamp (or anything powered by a plug) into an AC outlet, energy flows from the outlet into the device, not electrons.
 * **Eletcric power** - is the rate at which electric energy is converted into another from such as mechanical energy, heat, or light.
 * **Eletcric power** - current X voltage
 * A kilowatt is 1000 watts.
 * **A watt** - 1 amp x 1 volt
 * If a lamp rated at 120 watts operates on a 120 volt line it will draw a currnent of 1 amp
 * 120 watts= (1 amp) x(120 volts)
 * 60 watt= (0.5 amp) x (120 volts)
 * this relationship becomes a practical matter when you wish to know the cost of electrical energy, which varies from 1 cent to 10 cents per kilowatt hour, depending on location and time of year.
 * a kilowatt is 1000 watts
 * **a kilowatt**- hour represents the amount of energy consumed in 1 hour at the rate of 1 kilowatt.
 * therefore if the price of energy is 10 cents per kilowatt- hour, a 100 watt bulb will cost about 1 cent per hour
 * a toaster or iron or refrigerator or PS2/3/Xbox/Wii will draw more current and therefore more power costing much more to operate for the same amount of time.