Electrify Me! Electricity Basics
Matter and Electricity n Matter can be broken down into: n Conductors: electrons flow easily. Low resistance. n n Semi-conductors: electron can be made to flow under certain circumstances. Variable resistance according to formulation and circuit conditions. n n Wire, metals, electrolyte (salty water) Computer chips, cell phones Insulator: electrons flow with great difficulty. High resistance. n Rubber, plastic, wood, air
Basic Electricity n Electricity is the flow of electrons from one place to another. Electrons can flow through any material, but does so more easily in some than in others. How easily it flows is called resistance. n The resistance of a material is measured in Ohms (W).
Amps and Volt n The flow of electrons is called current, and is measured in AMPS. One amp is equal to a flow of one coulomb of electrons per second through a wire. n Making electrons flow through a resistance requires an attractive force to pull them. This force, called Electro. Motive Force or EMF, is measured in volts. n A Volt is the force required to push 1 Amp through 1 Ohm of resistance.
Electrical Power n As electrons flow through a resistance, it performs a certain amount of work. It may be in the form of heat or a magnetic field or motion, but it does something. This work is called Power, and is measured in Watts. n One Watt is equal to the work performed by 1 Amp pushed by 1 Volt through a resistance.
Terms of Endearment n AMPS is amount of electricity. n VOLTS is the Push, not the amount. n OHMS slows the flow. n WATTS is how much gets done.
The Voltage Formula n Voltage (V) is related to current (I) and resistance (R) by Ohm’s Law: V = IR n SO, as the resistance of a material increases, what will happen to the current if the voltage stays the same?
The Voltage Formula n OK, let’s take it the other way, if the resistance is reduced, what happens to the current? V = IR n Since the current is the flow of electrons, what would happen to the flow of electrons in a short circuit when the resistance drops toward 0 W?
The Power Equation Power = VI n The formula for Electric Power is sometimes called the West Virginia equation. n Watts = Volts * Amps n A kilowatt = 1000 watts n The amount of energy it would take to provide 1 k. W of electricity for an hour is a kilowatt-hour (k. Wh) (or W=VA)
Working with Circuts EXAMPLE: n A 12 volt battery in a car is powering a 5 amp circuit to run the windshield wipers. What is the resistance of the wiper motor?
Working with Circuits EXAMPLE: n An air-conditioner is rated at 1000 W. @ 120 V. At an EMF of 120 volts how much current will it draw? 1000 W. / 120 V. = 8. 33 A. n How much power would it take to power this air-conditioner for a week, at 12 hours a day? n If electricity costs ~ $ 0. 20/k. Wh, how much will it cost to run the air conditioner each week?
Working with Circuits EXAMPLE: n How many watts of power can be supplied on a 15 amp house circuit with a 120 volt power supply? n How many 75 watt light bulbs can be on that circuit? n What is the resistance (in ohms) of each light bulb?
Working with Circuits EXAMPLE: n How much current is running through a 20 W resistance in a refrigerator? (120 vlts = house current) n If electricity costs ~ $ 0. 20/k. Wh, how much will it cost to run the refrigerator each week?
AC 7 DC There are two different form of electricity we use: n DC or Direct Current n AC or Alternating current
AC 7 DC n DC or Direct Current n This is a simple pathway of electrons moving from a negative electrode to positive one. n Most battery operated devices are DC n The power is smooth, and easily regulated, but resistance builds over distance in a wire.
AC 7 DC n AC or Alternating Current n House current in the US is AC (In Europe it is DC) n Here the flow of electrons move one way, and then reverse themselves. In the US the electrons cycle back and forth at a frequency of 60 cycles /second (Hertz: Hz) n Using a transformer, the voltage of AC current can be shifted to minimize resistance, and be sent far distances. The power is not as smooth and often is converted to DC inside electric devices.
AC 7 DC Single vs. 3 -Phase power n House current is 100 -120 Volts single phase n 220 Volts is also available for domestic use n 220 Volt 3 -phase power is smoother and is preferred for industrial use.
AC 7 DC This is a 120 Volt House socket
22 O Volt House socket
Fuses vs. Circuit breakers
Fuses When a fuse “blows” the heat from the overloaded current melts the lead connection, breaking the circuit
Fuses
But what about Circuit Breakers?
Circuit Breakers
How does a Circuit breaker work? n A circuit breaker is basically just a coil of wire around a metal rod. n Current running through the wire creates a magnetic field through the metal rod. n An overload increases the magnetic force so that it pulls the switch open, stopping the current.
How does a circuit breaker work? n This is a cut away of an actual house circuit breaker n When a circuit breaker flips off, push the switch all the way into the off position to reset, and then to the on position.
Replacement circuit breakers n Circuit breakers like these are available to retrofit older fuse panels in houses.
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