No matter what you wish to study related to electrical engineering, electronics, communications, power, hardware design or anything else there are some things you MUST know. Whether you intend to transmit Tera-watts of power from one part of your country to the other, or just one millionth of billionth from one processor core another the first thing you must know is the Ohm's law. Then, Kirchhoff's current and voltage law.
Before we start with Ohm's law, let's take a look at a few definitions. If you think you know these things fairly well, you may skip this section
Electrical Charge: An electrical charge is a property of an object that makes if apply force to another object with charge. Ok, you might be like, what the! you can't define charge with another charge it's like instead of saying a phone is something you talk through, I say a phone is a phone. Well, I didn't say a charge is a charge, I said it applies force to another one. You see a charge is kinda a fundamental property of particles. And for a long time the only way you could even realize that charge existed is the way they interacted with other charged particles. Now how does a charge actually apply force to another one, well we'd have to go into quantum mechanics (which I am not very good at), specifically QED which I won't (more like can't) discuss here. For now, know there are two kinds of charges, positive and negative. And opposites attract and same ones repel each other. There is a law called Coulomb's law. I highly recommend that you look that up and at least understand the basic equation. Also, one thing I have to mention is that the unit of charge is a Coulomb (C).
Electrical Field: Simply put an electric field is the region of space surrounding electrically charged particles. Right. So we don't know what a charge is clearly, but we are trying to define what it does to the space around it? Well, I don't like to think of the electrical field as anything physical. Think of this electrical field as the amount of strength it can apply on another other at some other location (This is actually electrical field density, but don't worry about that). The 'strength' is the electrical field of that location (or point to be exact). So if you put a charge of one coulomb at some point near another charge, the amount of force the 1C charge 'feels' is the amount of electrical field of that point.
Potential difference: Potential difference between two points is defined by the amount of work needed to move an unit charge from one point in an electric field to another. The unit of potential difference is voltage, and it is probably the single most important unit electrical engineer's use. Apart from the awesome (not really) definition I just gave, the other way to think of potential is the 'work' you have to do to take an electrical charge through the 'strength' field (electrical field). The easiest way to relate to potential difference is with altitude (how high up something is). The higher a place is, the more work you have to do to take a heavy object to that place. And if you let it go the object will drop by itself to a place of lower altitude. Now potential difference is more important than potential, why? Well, let's take a look at altitude again. You say the altitude of something is say, 2m without giving a reference first. Where are you 2m high from? Maybe from the ground. You say the ground is 0m high, so anything that is 2m high from the ground is 2m high. Well the ground is relative. If you were living underground then calling the surface 0m would be problematic. If you were stationed as a space marine on a space station (I really, really hope someone reading this will be) then calling the ground 0m would be impractical. Same goes for potential difference. There is no absolute 'potential'. Sure some say the point infinity has 0 potential, but since we can't go there let's just forget potential and deal with potential difference, the same way we deal with altitude. The same way ground has 0m altitude, we think one point in circuits as the 'ground' which has 0V (volt) potential. If then we say any other point has 5V potential then it only means that the potential difference of that point with respect to the ground is 5V. When electrical engineers use voltmeters, they don't measure the voltage (or potential) of one point, only the voltage difference of two points.
Electrical Current: Electric current is a flow of electric charge through a conductive medium. The unit for electrical current is Amperes (A). 1A = 1C/s
Ohm's law is simple. It states that the current through a conductor between two points is directly proportional to the potential difference across the two points. (well it's may not seem simple from this sentence). So basically Ohm's law says that current goes from a point of higher potential to a point of lower potential, who would've guessed! So, if you take a conductor (say a piece of copper wire) and create potential difference between two points of the conductor (say by using a battery), current would flow through the conductor from the point of higher potential to the point of lower potential. But don't try this at home. No seriously, DON'T connect two ends of a copper wire using a battery, why not? I'll tell you later.
Now, this law of Ohm, in terms of mathematics goes like this: I ∝ V, where I is the current and V is the potential difference.
It is also written like this V = I R, R is called the resistance of the conductor. The more resistance a conductor has the less current will flow through it for a given amount of potential difference. The unit of resistance is ohm.
Say a conductor has resistance of 1ohm. If we create a potential difference of 10V, then the current flowing would be 10V/1ohm = 10A. If another conductor had resistance of 2ohm, creating a potential difference of 10V across it would cause a current, 10V/1ohm = 10A.
I = V/R, can be derived from V = I R
Learn this formula very carefully, this is the single most important law in electrical engineering. If you know any two of V, I or R you can find the other one
Now, what would happen if you connected two ends of a battery (of say 1.5V) using a copper wire. The wire is a very good conductor, which means it has very low resistance. The resistance of a 1 foot 12 gauge wire is about .002ohm. So the current I = 1.5V/.002ohm = 750A (!). Now you may not realize how high that is, but trust me it is REALLY high. Even though the battery won't be able to supply that much current, it can still get pretty high and the wire can get very hot and you can even burn yourself. So don't do it. Never 'short out' a battery using a wire, of any kind!
Just a little more thing before I finis. Resistance depends on the property of the material used as well as the shape of the material used. R = ρL/A. The ρ is called resistivity and it is unique for a given material. L is the length of the material and A is the cross section. So the longer a wire is the more resistance it has. And the thicker it is the less resistance it has.
This post turned out more textbook-ish than I wanted to. Nevertheless, I am publishing it. I will try to make the next one less textbook-ish. In the mean time keep electrical engineering!
Before we start with Ohm's law, let's take a look at a few definitions. If you think you know these things fairly well, you may skip this section
Electrical Charge: An electrical charge is a property of an object that makes if apply force to another object with charge. Ok, you might be like, what the! you can't define charge with another charge it's like instead of saying a phone is something you talk through, I say a phone is a phone. Well, I didn't say a charge is a charge, I said it applies force to another one. You see a charge is kinda a fundamental property of particles. And for a long time the only way you could even realize that charge existed is the way they interacted with other charged particles. Now how does a charge actually apply force to another one, well we'd have to go into quantum mechanics (which I am not very good at), specifically QED which I won't (more like can't) discuss here. For now, know there are two kinds of charges, positive and negative. And opposites attract and same ones repel each other. There is a law called Coulomb's law. I highly recommend that you look that up and at least understand the basic equation. Also, one thing I have to mention is that the unit of charge is a Coulomb (C).
Electrical Field: Simply put an electric field is the region of space surrounding electrically charged particles. Right. So we don't know what a charge is clearly, but we are trying to define what it does to the space around it? Well, I don't like to think of the electrical field as anything physical. Think of this electrical field as the amount of strength it can apply on another other at some other location (This is actually electrical field density, but don't worry about that). The 'strength' is the electrical field of that location (or point to be exact). So if you put a charge of one coulomb at some point near another charge, the amount of force the 1C charge 'feels' is the amount of electrical field of that point.
Potential difference: Potential difference between two points is defined by the amount of work needed to move an unit charge from one point in an electric field to another. The unit of potential difference is voltage, and it is probably the single most important unit electrical engineer's use. Apart from the awesome (not really) definition I just gave, the other way to think of potential is the 'work' you have to do to take an electrical charge through the 'strength' field (electrical field). The easiest way to relate to potential difference is with altitude (how high up something is). The higher a place is, the more work you have to do to take a heavy object to that place. And if you let it go the object will drop by itself to a place of lower altitude. Now potential difference is more important than potential, why? Well, let's take a look at altitude again. You say the altitude of something is say, 2m without giving a reference first. Where are you 2m high from? Maybe from the ground. You say the ground is 0m high, so anything that is 2m high from the ground is 2m high. Well the ground is relative. If you were living underground then calling the surface 0m would be problematic. If you were stationed as a space marine on a space station (I really, really hope someone reading this will be) then calling the ground 0m would be impractical. Same goes for potential difference. There is no absolute 'potential'. Sure some say the point infinity has 0 potential, but since we can't go there let's just forget potential and deal with potential difference, the same way we deal with altitude. The same way ground has 0m altitude, we think one point in circuits as the 'ground' which has 0V (volt) potential. If then we say any other point has 5V potential then it only means that the potential difference of that point with respect to the ground is 5V. When electrical engineers use voltmeters, they don't measure the voltage (or potential) of one point, only the voltage difference of two points.
Electrical Current: Electric current is a flow of electric charge through a conductive medium. The unit for electrical current is Amperes (A). 1A = 1C/s
Ohm's law is simple. It states that the current through a conductor between two points is directly proportional to the potential difference across the two points. (well it's may not seem simple from this sentence). So basically Ohm's law says that current goes from a point of higher potential to a point of lower potential, who would've guessed! So, if you take a conductor (say a piece of copper wire) and create potential difference between two points of the conductor (say by using a battery), current would flow through the conductor from the point of higher potential to the point of lower potential. But don't try this at home. No seriously, DON'T connect two ends of a copper wire using a battery, why not? I'll tell you later.
Now, this law of Ohm, in terms of mathematics goes like this: I ∝ V, where I is the current and V is the potential difference.
It is also written like this V = I R, R is called the resistance of the conductor. The more resistance a conductor has the less current will flow through it for a given amount of potential difference. The unit of resistance is ohm.
Say a conductor has resistance of 1ohm. If we create a potential difference of 10V, then the current flowing would be 10V/1ohm = 10A. If another conductor had resistance of 2ohm, creating a potential difference of 10V across it would cause a current, 10V/1ohm = 10A.I = V/R, can be derived from V = I R
Learn this formula very carefully, this is the single most important law in electrical engineering. If you know any two of V, I or R you can find the other one
Now, what would happen if you connected two ends of a battery (of say 1.5V) using a copper wire. The wire is a very good conductor, which means it has very low resistance. The resistance of a 1 foot 12 gauge wire is about .002ohm. So the current I = 1.5V/.002ohm = 750A (!). Now you may not realize how high that is, but trust me it is REALLY high. Even though the battery won't be able to supply that much current, it can still get pretty high and the wire can get very hot and you can even burn yourself. So don't do it. Never 'short out' a battery using a wire, of any kind!
Just a little more thing before I finis. Resistance depends on the property of the material used as well as the shape of the material used. R = ρL/A. The ρ is called resistivity and it is unique for a given material. L is the length of the material and A is the cross section. So the longer a wire is the more resistance it has. And the thicker it is the less resistance it has.
This post turned out more textbook-ish than I wanted to. Nevertheless, I am publishing it. I will try to make the next one less textbook-ish. In the mean time keep electrical engineering!
