CHAPTER FOUR ohms law these units and symbols for electrical quantities will become very important to know as we begin to explore the relationship between them and circuits. The first and perhaps the most important relationship between current voltage and resistance is called ohms law discovered by George Simon own and published in his 1827 paper, the galvanic circuit investigation mathematically only ohms principle discovery was that the amount of electric current through a metal conductor in a circuit is directly proportional to the voltage impressed across it for any given temperature. Also, the current is inversely proportional to the resistance of the wire or the resistance in the circuit. Omen, press two discovery in the form of a simple equation describing how voltage current and resistance are interrelated. Here, voltage is equal to current times resistance. This is an algebraic expression of course, where voltage E is equal to the voltage and i is equal to the current and r is equal to the resistance.

Using algebraic techniques we can manipulate this equation into two variations, solving for AI and solving for R respectively. If EA equals IR, then I would equal EA over R and R would equal P over i. What this is telling us that given any To have these three unknowns, the third one can be calculated. This is referred to as ohms law. And this is probably the simplest and most important relationship in any and all electric circuits. Let's look at an example.

A light, or a lamp bulb, which we'll call a load is connected across a battery. It is given that the load or the light is three ohms and is connected across a 12 volt battery. What is the current that will flow in this circuit? It is predicted by ohms law, the current will be equal to the voltage divided by the resistance or 12 divided by three, which gives us four amps. Let's look at another example with just a slightly different twist. Twist being that we are given the current and the voltage.

And we want to know what the resistance in the circuit is or the resistance of the lamp if the current is four amps driven by a 36 volt battery. And what would the resistance be, the resistance will be given by the voltage divided by the current or 36 divided by four, which is nine ohms. ohms law is a very simple and useful tool for analyzing electric circuits. It is used so often in the study of electricity and electronics that it needs to be committed to memory. For those who are not yet comfortable with algebra, there's a trick to remembering how to solve or remembering where the variables belong in the equation. First arrange the letters E and R in a triangle Like this, then remember that v is always the numerator above I or R. Another trick is to just think logically, current always goes up with voltage and down with resistance.

Or another way to remember it is with this cartoon, which is appeared in many ways, shapes or form. But you got three fellows that are that are attempting to work on the Mr. hab and Mr. amp is being restricted by Mr. ohm, and he's being pushed by Mr. Volk. conductance is the ability of an element to conduct current. It is the reciprocal of resistance, therefore conductance if given by g is equal to one over R. It's measured in quantities called Siemens. And in terms of voltage and current, g is equal to AI over V, which is the opposite to resistance or the inverse to resistance. This term is seldom used, but it should be recognized if you do come across it there are rare times when conductance is used rather than resistance, but you should know what it means.

So listens chapter four,