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Ohms Law

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Linda Raynes

on 24 September 2012

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Transcript of Ohms Law

Ohms Law Probably the most important mathematical relationship between voltage, current and resistance in electricity is something called
“Ohm’s Law”. OHM'S LAW
V = I x R,
I = current,
V = voltage
R = resistance
Depending on what you are trying to solve we can rearrange it two other ways.
I = V/R
R = V/I Ohm's Law tells us that the electrical current flowing in a circuit is directly proportional to the voltage and inversely proportional to the resistance. What does that tell you????? Electricity is a term used to describe the energy produced (usually to perform work) when electrons are caused to directional (not randomly) flow from atom to atom. This movement of electrons between atoms is called electrical current Electricity can be very dangerous and it is important to know something about it in order to work with it safely. The flow of electrons is measured in units called amperes. . An amp is the amount of electrical current that exists when a number of electrons, having one coulomb (ku`-lum) of charge, move past a given point in one second. A coulomb is the charge carried by 6.25 x 10^18 electrons. 6.25 x 10^18 is scientific notation for 6,250,000,000,000,000,000. That is a lot of electrons moving past a given point in one second! Current An ammeter is an instrument used to indicate how many amps of current are flowing in an electrical circuit. http://www.ndt-ed.org/EducationResources/HighSchool/Electricity/amperage.htm Voltage We also need to know something about the force that causes the electrons to move in an electrical circuit. This force is called electromotive force, or EMF. How do we create this “electrical pressure” to generate electron flow? There are many sources of EMF. Some of the more common ones are: batteries, generators, and photovoltaic cells, just to name a few. Batteries are constructed so there are too many electrons in one material and not enough in another material.
The electrons want to balance the electrostatic charge by moving from the material with the excess electrons to the material with the shortage of electrons. However, they cannot because there is no conductive path for them to travel.
If these two unbalanced materials within the battery are connected together with a conductor, electrical current will flow as the electron moves from the negatively charged area to the positively charged area. Caution: you should never connect a conductor to the two ends of a battery without making the electrons pass through something like a light bulb or resistance which slows the flow of currents. If the electrons are allowed to flow too fast the conductor will become very hot, and it and the battery may be damaged. To understand how voltage and amperage are related, it is sometimes useful to make an analogy with water http://phet.colorado.edu/en/simulation/ohms-law Another way of saying this is: without EMF or voltage, there will be no current. Also, we could say that the free electrons of the atoms move in random directions unless they are pushed or pulled in one direction by an outside force, which we call electromotive force, or EMF. Resistance can be both good and bad. If we are trying to transmit electricity from one place to another through a conductor, resistance is undesirable in the conductor. Resistance causes some of the electrical energy to turn into heat so some electrical energy is lost along the way. However, it is resistance that allows us to use electricity for heat and light. Resistance There is another important property that can be measured in electrical systems. This is resistance, which is measured in units called ohms. Resistance is a term that describes the forces that oppose the flow of electron current in a conductor. If we use our water analogy to help picture resistance, think of a hose that is partially plugged with sand. The sand will slow the flow of water in the hose. We can say that the plugged hose has more resistance to water flow than does an unplugged hose. If we want to get more water out of the hose, we would need to turn up the water pressure at the valve. The same is true with electricity. Materials with low resistance let electricity flow easily. Materials with higher resistance require more voltage (EMF) to make the electricity flow. it is sometimes useful to add components called resistors into an electrical circuit to restrict the flow of electricity and protect the components in the circuit.

Resistance is also good because it gives us a way to shield ourselves from the harmful energy of electricity When we connect various components together with wires, we create an electric circuit. Like this Circuit diagrams are a pictorial way of showing circuits. Electricians and engineers draw circuit diagrams to help them design the actual circuits. Here is an example circuit diagram Next time you will be creating your own circuits from a circuit diagram as you learn about what series and parallel circuits are Ammeter Voltmeter battery switch
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