Electric Current, Voltage, and Resistance

Life without electricity <GASP!> What would life be like without electricity??? Life Without Electricity

Producing Electric Current Generators The “nuts and bolts” Anytime you turn on something with power, you complete a circuit and current, in the form of electrons is sent through a wire. The source of this energy is almost always some sort of generator. A generator is just a device that moves a magnet near a wire to create a steady flow of electrons. The action that forces this movement varies greatly, ranging from hand cranks and steam engines to nuclear fission, but the principle remains the same. Let’s use water flowing from a pipe (say, to water our garden) as an analogy. The source of the water – the generator – is the pressurized tank.

Electric Current: The rate of flow of electric charge or the number of electrons in motion. Symbolized by: I (capital i) Measured in coulombs per second 1 coulomb per second is an ampere (A) 1 C/s = 1 A For instance, a generator spinning at 1,000 rotations per minute might produce 1 amp (at 6 volts). The 1 amp is the number of electrons moving 1 amp physically means that 6.24 x 1018 electrons move through a wire every second We can measure it with a device called an ammeter. When watering the garden, the current is represented by: the amount of water that flows out of the pipe.

Electrical Pressure Danger! Voltage By definition, the electric potential difference is the difference in electric potential (V) between the final and the initial location when work is done upon a charge to change its potential energy. In equation form, the electric potential difference is: work/charge Voltage = electrical pressure that pushes charge or electrons along It is a flow of charged particles. Charges flow from high voltage to low voltage Voltage difference (V) is the push that causes charges to move Voltage is measured in volts The wall outlets in your home or the school are 120V Flow of current stops when the differences are equal. How could you keep flow moving?

Flow of charge So … Back to our garden analogy … what is the voltage? To get more water to come out you increase the pressure in the pump. The same is true with an electrical system – increasing the pressure (voltage) results in a greater flow of charge (current)

Resistance: The tendency for a material to oppose the flow of electrons. This happens because electrical energy is changed into thermal and light energy. Causes electric current to lose energy as it moves through the filament Resistance decreases the amount of e- that can flow through a conductor Increase resistance = decrease current Resistance is measured in ohms (Ω) Electrical conductors have a lower resistance than insulators.

RESISTANCE IS Not Futile. It's Voltage Divided by Current. The size, length, temperature and the conductivity of the material of the wire all affect resistance Electrons move more efficiently through thick wires than thin wires (the thicker the wire, the less resistance). The longer the wire, the greater the resistance because more collisions will occur over a greater length of wire. Materials classified as conductors, such as (in order of greatest conductivity) silver, copper, gold, aluminum, iron, platinum, and lead will all have low resistances. Where are the first 3-4 all commonly used? Wiring all over your house, car, electronics, etc. The resistance will increase with increasing temperature Think about it like traffic on a highway … As there become more cars trying to move quickly, it becomes harder for them to all move without colliding. In terms of electrons, the hotter it gets, the more collisions there are The more collisions that occur, the more they are slowed down.

Electric Resistance Once again with the garden analogy: If we increase the diameter of the hose, what happens? More water comes out of the hose This is like decreasing the resistance of an electrical circuit. If more water comes out what can we say about the current? It increases!!! What if we make the hose longer? Less water will come out because the resistance is increased

The analogy … Revisited Let's put it all together!

Current = Voltage Difference Resistance OHM’S LAW: Current = Voltage Difference Resistance

OHM’S LAW AND ELECTRIC SHOCK Touching surfaces of differing potential you become a pathway for current Electric shock can overheat (cook) tissues or disrupt nerve functions = disrupt breathing…remove with non-conducting material and apply artificial respiration

AC/DC Batteries, fuel cells and solar cells all produce something called direct current (DC). The positive and negative terminals of a battery are always, respectively, positive and negative. Current always flows in the same direction between those two terminals. The power that comes from a power plant, on the other hand, is called alternating current (AC). The direction of the current reverses, or alternates, 60 times per second (in the U.S.) The power that is available at a wall socket in the United States is 120-volt, 60-cycle AC power.

But what happens when the flow of charges between two things with a potential difference becomes balanced out? If you want to keep the electricity going, you would need to keep the flow going by maintaining a potential difference? This is done by pumping charged particles from the lower potential that became balanced by gaining charges back to the higher potential that lost charges.

So … which will be your demise? What will be the cause of your ultimate demise if you happen to come in contact with a high voltage fence? It won’t be the resistance … which your body actually has a high amount of. The amount of current pushed out is what actually causes death. Without the large potential difference (voltage) there wouldn’t be a large current flowing through you. Your demise!

Electrical Power The rate at which electrical energy is converted to another form of energy Power = current x voltage Power = current2 x resistance Watts = Amps x volts

Calculating Energy: Depends on two things: Energy = power x time Power required How long the piece of equipment is used Energy = power x time E (kWh) = P (kW) x t(h) Unit is kilowatt-hr (kWh)