New Guy question about electronic component

  • #1
Hi hope someone could help me understand the workings of electronic components.

I think I am right in saying that all electronic components require energy for them to function.

If you connect a battery to the component to supply the energy then this is supplied from the electrochemical energy in the battery.

The battery pushes electrons up a potential difference through the circuit from - to +

Here I get a bit hazy

The electrons are pushed through the component and 'lose energy'? while they are travelling through it? This lost energy is used by the resistors, lcds etc to do 'their thing'.

What is different in the electron that leaves the neg terminal and reaches the pos terminal?

Is it in a lower energy state?

Also this electron that returns to the battery. Dosnt it go on to take part in a chemical REDOX reaction? How does that happen?

Why does it need to be in a lower energy state to work?

Sorry total confusion as you see. Id be grateful if someone could give me a heads up!

Neil
 

Answers and Replies

  • #2
247
2
It is hard to think of individual electrons in a circuit. A good way to get a basic understanding of "circuit flow" is to think of it like water. If you took a container with a hose fitted to the bottom and filled the container with water and put it on the roof, the water would have more potential energy than it would down on the ground. The height the container is off the ground is like a battery's Voltage. The amount of water in the container is like the battery's capacity. If you open a valve and the water flows through the hose, the rate of flow is like the battery's Current.

To extend this analogy to a circuit, if you had a small water wheel down on the ground, and you directed the flow of water so that it turned the water wheel, the amount of mechanical energy you could impart onto the water wheel would be limited by the potential energy in the water, and in reality the energy imparted would be somewhat less than the potential energy it had when it was up on the roof. Some of the energy would be lost from splashing, and the water would still have some energy when it left the water wheel.

If you captured the water exiting the water wheel; when the container on the roof was empty, you would have to carry the water back up to the roof and place it back into the container if you wanted the water wheel to continue turning. Climbing up to the roof with the water would be a lot more "work" than just turning the water wheel by hand, so it follows that you are getting less work out of the system than you are putting in, and it turns out that this is ALWAYS true.

I understand the desire to "grasp" every facet of how a circuit works, but electricity requires a fairly high level of abstract thought and is best understood through mathematics. It also helps to think of circuits as "black boxes". For instance the "battery" might be one "black box". To understand a circuit all you need to know about the "black box" marked "battery" is its Voltage and Source Resistance (and, perhaps, Capacity). How it provides these characteristics is not important to understanding how a circuit might perform. As an example:

If you have a 12V power source rated @ 10A, you can calculate the source resistance as 12V/10A = 1.2 Ohms. Assuming this power source is adequate to drive your circuit, it makes no difference if it is a battery, a traditional line transformer power supply, a SMPS power supply, a solar panel or a dynamo.

Similarly, if you have a resistance rated at 1000 Ohms with a maximum power dissipation of 1/4W, how the resistor is constructed is not important to understanding how it works. (Well, that is NOT entirely true, but for our purposes here it is true enough). If you connect a 1000 ohm resistance to a 12V source, a current of 12V/1000 = .012A will flow, and the resistor will dissipate 12V * 0.012A = 0.144W in the form of heat. (Heat = Energy Loss).

Hope that helps a bit.

Fish
 
  • #3
Thanks this was very helpful! I guess I nerd that I am - am actually interested in the black box stuff that is not really important for everyday use. I'd kind of like to get away from the waterfall analogy to try and understand what is actually taking place.

I thought that it is electron flow that causes the circuit to work- charged particles moving in a potential difference field?

Is this not what happens?

If I can stay with a battery connected to a circuit say a 100 ohm resistor for arguments sake.

As far as I understand:

To make the chemical reaction take place within the battery the positve and negative terminals must be connected together. This allows the redox reaction of the two chemicals to take place.

The whole point of this reaction is to release electrons with a certain energy level into the circuit. Each electrons energy can be measured in Joules. By the time the electron has returned to

When it comes to rating the battery as a voltage 1.5 volts potential difference. This means err.. not sure actually maybe that each electron will move with a certain speed, have a certain starting energy?

Also the idea of current draw on the battery is causing me confusion. Does a circuit with a higher resistance load pull more charged particles out of the battery per second. In other words make the chemical reaction take place faster.. that dosnt make sense.

If the pos and neg terminal of the battery is connected together, does the chemical reaction always take place at the same rate and hence release the same amount of electrons into the circuit. Or are there circumstances that cause the reaction to take place at a slower rate?

Im trying bridge the gap in my understanding between the old pipe line analogy and what actually takes place. I know its complicated but heh.. i guess its better to understand things properly!
 
  • #4
247
2
The problem is you are attempting to grasp two very different concepts simultaneously, hence the water flow analogy. You should really pick one concept and pursue it until you are comfortable with it, then pursue the other concept.

Understanding electricity and circuits is independent of understanding HOW the electricity is generated.

Understanding how batteries produce electricity is independent of understanding how that electricity is used.

One more analogy: If you want to know how to bake a cake, you do not need to understand Farming. Understanding farming is a fine and wonderful thing that should be pursued if one so desires, but if your goal is to bake a cake, you need to focus on the ingredients and the process, not how the ingredients are sown and harvested.

Now, to Voltage (regardless of how it is generated):

http://en.wikipedia.org/wiki/Voltage

And Current (Independent of Voltage):

http://en.wikipedia.org/wiki/Ampere

I would strongly recommend you read through this:

http://www.allaboutcircuits.com/vol_1/chpt_1/7.html

Finally, Voltage is a measure of the energy the electrons have, current is a count of how many electrons flow in a specific period of time. If you think of Voltage as "Height" and Current as "Mass", then it should be clear that dropping a pea from the dinner table to the floor will do less "damage" than dropping an anvil from the Empire State Building.

If you dropped the pea from the Empire State Building, it would fall further and reach a higher velocity than it would from the dinner table (similar to voltage). If you drop a larger mass (the anvil) you have more "flow" (similar to current). In all cases, until the object is dropped, nothing happens. This is Potential Difference, and it is similar to Potential Energy. That is, the object has potential energy, the amount of potential energy it has is a function of its height, or, in the case of electricity, Voltage.

...I don't know if I am helping you or not.....

Fish
 
  • #5
10
0
I'm not mathematically inclined, but I can explain it at your level. First, the resistor: basically, resistors allow electrons to flow through but the material structure forces the electrons to have many interruptions and ricochets to the flow. Like pouring pingpong balls down a mountainside. Think of the the noise of an avalanche. As the electrons work their way through (the voltage is like the gravity down the mountain, it is the push that makes them "want" to go that-a-way) all that "noise" they make vibrates the atoms they are "colliding" with. And that is what heat is: vibrating atoms. It works its way to the surface of the resistor where your finger is, and you feel the heat. Also some of the vibration is expressed as electromagnetic waves, which leave the surface as infrared radiation. Get the heat hot enough, and some of the waves are visible red. That is why heater coils glow orange. Put your hand by it, what you feel is the invisible infrared warming your hand.
Now batteries I'm a little more vague on, but here is some idea: Most batteries consist of a metal cathode (the negative pole, the electron source for the external circuit) and a less reactive anode (in a common battery, a carbon rod) separated by an acid or alkali (liquid in some battery types, just wet mush in others, actually molten in a few, depending in the design). This part is called the "electrolyte." The electrons in the metal have an energy level that is inherent in the fact that it is a refined metal. The work done to make it into metal out of its ore has "lifted" the electrons to an "elevated" position, like the pingpong balls at the mountain top. The chemical reaction at the metal-to-electrolyte interface pulls the metal atom loose and tosses the electron back to the metal remaining. Those electrons accumulate so the metal is charged with excess electrons, that is, it is negatively charged, typically just 1 to 3 volts depending on the chemistry, which frankly isn't very much. This voltage produces a electric field that brings the chemistry to a halt, else the battery would be useless within a few minutes as the metal corroded to nothing. But if you connect a circuit so the charge can flow "down" to the other side, to the anode, where the flow back in is not inhibited by chemistry, then the electrolyte can toss those electrons as fast as the reactions can proceed (as it claims metal atoms). This can go on until the metal is all gone or the electrolyte gets choked on metal. Which is now oxidized, corroded, and no longer metallic. Then the battery is dead. If a fresh battery can supply one "amp" of electrons for one hour, that means 6.241 × 10^18 electrons have flowed every second for 3,600 seconds. If it took one metal atom to "die" to supply each electron, that's a chunk of metal. Probably less than an ounce. You chemistry types can say exactly how much.
It is the chemistry, the reaction between the electrolyte and the metal, that determines the voltage, and the amount of metal (and the electrolyte's ability to absorb the metal) that determines the capacity. And the maximum rate of reaction that limits how many electrons can be supplied at a time. If you short the battery out with a very low resistance, it will supply the electrons absolutely as fast as it can. Some batteries will explode if you do this because the reaction also produces some heat.
Rechargeable batteries just means you can push the electrons back through reverse to force the electrolyte to put the atoms back up into metal form. In other words, you are refining metal ore, pushing the pingpong balls back up to the mountaintop. Once recharged, you're ready for the next avalanche.
This explanation doesn't cover every battery chemistry, as I'm sure someone will point out.
 
  • #6
Thanks that was very informative.

I had no idea that a battery had an electric field that stopped the reaction when the terminals are not connected together.

I think Im really interested in the border where the terminals are connected to the circuit.

If the battery is shorted + connected to - with minimal resistance then the chemical reaction takes place at its maximum rate.

If there is a load what slows the battery reaction down? Is it that the electrons have to struggle to get through the resistance and so there is a kind of electron back up at the terminals waiting for their turn to get through the circuit.

But that dosnt make sense as if you used a more powerful battery it would be able to supply additional electrons to 'overcome the resistance'

?

I guess Im looking for a formula to determine how the external resistance determines the rate at which the chemical reaction takes place and electrons are supplied to the circuit.

Can you explain a bit more about how this electric field that is present when the terminals are not connected and how it is broken when they are connected.
 
  • #7
10
0
The battery voltage, say 1.5 volts, is the electric field that the reaction is controlled by (and produces too). When you load the battery, the voltage will drop ever so slightly, which allows the reaction to begin proceeding. The more load you put on the battery, the lower the voltage (even though it may be only a small fraction of a volt) and the reaction speeds up accordingly. A dead short of course reduces the voltage to whatever the battery can produce at maximum reaction speed. A bigger battery will sustain a higher voltage into a short. Let's say the wire you are shorting with has a resistance of .05 ohms. A small battery may be able to sustain .2 volts into that, which will push a current of 4 amps (E / R = I, where "E" means volts. E is for "electromotive force" and "I" means current [I forget why "I" and not "A" or "C", but those are the standard letters to use for this]; .2/.05 = 4.) That is .8 watts (E x I = W, so .2 x 4 = .8), and you can feel the heat. A bigger battery say can hold up 1 volt, or 5 times the current, at 20 amps. That is 20 watts (1 volt x 20 amps = 20 watts) and a smallish wire will melt in two. A bigger wire may cause the battery to blow up (that's why dropping a wrench across a car battery is a Very Bad idea. Acid splatter is Not Friendly).
 

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