A foot is about a nanosecond.
But, the speed of light is exactly 299792458 m/sec
Am I missing something? All of the speeds given here for the speed of light is for the speed of light in a vacuum.
I may be wrong but I think the speed of light (or electricity in this case) in the circuitry of a CPU is considerably slower (although still quite fast).
I’ll see if I can find a cite unless someone (hopefully) beats me to it.
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*Originally posted by Whack-a-Mole *
**
I’ll take a stab at it…
Ever see a metronome? That’s basically what the clock frequency in a CPU does…it measures off cycles. Everything moves ‘forward’ one step on each ‘tick’ of the clock.
[quote]
Ok I getting a picture of a lot of things from all the responses but let me try again.
Say I attach a solenoid to a support,when I apply current to it the plunger shoots out and pushes a hinged lever which in turn releases the current to the solenoid so that the spring in the solenoid snaps it back in which in turn lets the hinged lever return to it’s place and re instates the current and out pops the plunger again to repeat the action continually,hence we have a simple on off cycle that can be adjusted by more power/bigger solenoid and/or closing the gap between the plunger at rest and the hinged lever.My question,how is that done electronically?
Acutally, Moore’s law refers to transistor density, which has real limits in physics (transistors can only get so small) - although it does look promising that Moore’s law can continue for awhile into the future (Experimental transistors are having their size measured in atoms)
Performance tends to increase much slower than transistor density; probably due to software issues and the fact that most of what people wait on today isn’t the CPU but rather various components of the I/O subsystem (which of course will benefit from improvments in solid-state technology, but I digress)
You seem to be describing a simple mechanical oscillator. So you’re asking how to create an electrical oscillator? The simplest one using transistors is the astable multivibrator, and the schematic can be seen at the very bottom of this page. The two transistors take turns switching hard on & off, and you can manipulate the duty cycle by adjusting the values of R. The output on the collectors of the transistors is a simple square wave, switching between zero and the supply voltage. The LEDs are optional. If transistors are too passé, use a 555 or 565 timer chip to get the same thing.
You seem to be describing a simple mechanical oscillator. So you’re asking how to create an electrical oscillator? The simplest one using transistors is the astable multivibrator, and the schematic can be seen at the very bottom of this page. The two transistors take turns switching hard on & off, and you can manipulate the duty cycle by adjusting the values of R. The output on the collectors of the transistors is a simple square wave, switching between zero and the supply voltage. The LEDs are optional. If transistors are too passé, use a 555 or 565 timer chip to get the same thing. **
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Yes!!! now I think we’re getting some where :-)I see the circuit and can see how the current would light the leds.
Is it that the actual wave of the current going through it’s cycle i.e.plus through zero to minus is what is used to flash/cycle the lights?If that’s the case I think we can consider this thread sewn 
YOu can always try howthingswork.com which is the same as howstuffworks.com for more details.
The transistors simply act as switches, turning on and off. When one of the transistors is on, it completes a path for current flow from the negative side of the battery (in this case ground) to the positive attraction at V+, limited only by the 470[sym]W[/sym] resistors. The other components R and C are used to set the timing & duty cycle of the pulses.
This circuit is a poor source for a TTL clock running higher than 100KHz, I only provided it because of its simplicity.
[QUOTE]
*Originally posted by Attrayant *
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The transistors simply act as switches, turning on and off.
I understand that but what I don’t understand is how they do it,is it possible to explain in laymans terms as I did in my mechanical example?Like does something melt in the transistor,break the circuit and flow back down before it cools to repeat the purpose.does a mercury ball in a tube in the transistor bounce from side to side trying to get away from the current at each end hence forming an on off cycle?
Oh, in that case you’re looking for a short course in semiconductor physics. Transistor theory is complex, even when they are being used only as electronic switches.
To even begin to have a chance of explaining the oscillation cycle, we have to name the components. Let’s call the components on the left Q1 (the transistor), R1 and C1. On the right we have Q2, R2 and C2. We ignore the 470[sym]W[/sym] resistors because they are not a critical part of the timing circuit, they are there mainly to limit the current through the transistors & LEDs.
Each transistor is made to “turn on” when it is presented with a small positive voltage on its base electrode. For silicon transistors, this potential is six-tenths of a volt. So the cycle begins like this: Capacitor C2 begins to charge through Q1 and R2. After a short time (determined by the values of R and C), the negative side of C2 builds up enough of a charge to cause transistor Q1 to switch on. When Q1 turns on, it becomes a virtual short-circuit from collector to emitter, supplying the LED with a current source. At the same time, C1 is discharged causing transistor Q2 to shut off. Q1 and Q2 will always be in opposite states.
C1 then begins to charge through Q2 and R1… lather, wrinse, repeat. The cycle repeats, each transistor being “turned on” by a charging capacitor and then shutting off when the opposite transistor turns on.
Crystal clear, huh? This was not an easy circuit for me to describe in the classroom even given a chalk board & other visual aids. I am sure it is even harder to describe using text only. Pick up a book on semiconductor fundamentals, starting with diodes and then moving to basic transistor theory. Without knowing about how how the subatomic particles are actually behaving inside the semiconductor materials, it’s really very difficult to grasp the concept of electronic switching.
I’m not sure I can explain this in layman’s terms but…
Transistors by themselves are not oscillators. Transistors are basically devices that act kind of like electronically controlled switches. Consider a simple bipolar junction transistor, which has a base, a collector, and an emitter. If you apply current between the base and the emitter, you can control how much electricity flows between the collector and the emitter, kinda like controlling the flow of water through a hose with the valve. In linear things like stereo amplifiers, you want the control to be always in the middle, kind of like never turning the water all the way on or all the way off. In a computer and digital devices, you want the opposite, you want to turn the water valve all the way on for a logical 1 and all the way off for a logical 0.
There are a lot of ways to make oscillators. Computers tend to use quartz crystal, which has an electrical resonnance. I guess the best way to describe this is when you blow across an empty soda or beer bottle, you make a sound of a particular frequency, because that is the natural resonnance of the bottle.
In a transistor oscillator, what is basically happening is that you are relying on feedback. Imagine two guys each with a flag in their hands, that they can put up or down. The first guy says I’m going to do the opposite of whatever the other guy does, and the second guy says I’m going to do the same thing as the other guy does. So, the first guy raises his flag, and the second guy does the same thing, which causes the first guy to lower his, which then causes the second guy to lower his, making the first guy raise his, which makes the second guy raise his, etc. etc. How fast the flags go up and down is therefore a function of how fast each flag person can raise or lower their flag. In an electronic circuit this is the switching speed of the transistor. You can slow down the switching speed with capacitors (which are just a couple of metal plates), which take a while to charge up.
Achernar wrote:
<quantum mechanics nitpick>
As Achernar’s “(Classically speaking)” comment indicates, it is not really correct to say that an electron “circles around” or “orbits” a nucleus.
Rather, an electron exists in an energy state around a nucleus, in which there is a probability distribution as to where it will be found if you look for it. This probability distribution is spherical in the case of the innermost (“s”) orbitals, but is lobe-shaped and not symmetrical about the nucleus for the next higher (“p”) orbitals.
</quantum mechanics nitpick>
I think the last couple of answers have concentrated too much on the oscillator circuit that Attrayant mentioned as an example. I think what Virtually Yours is trying to grasp as per this quote:
His real question is how does a semiconductor work at a physical level that is, what physical change is it going through to switch on and off at such amazing speeds? I sort of kind of remember enough high school physics to have a reasonable idea of the answer to that question in my own mind, but I think it would probably be better if someone with a clearer grasp answered that question.
Basically, though, there is nothing so crude as a movement of a mercury ball or a melting/cooling cycle (which would be much too slow). The switching is done by movement of electrons to/from an interface between two materials in the semi-conductor, which interface will only conduct if the electrons are/are not positioned appropriately. Before I totally confuse the issue I will stop and leave someone with more knowledge to explain more detail. Or do a google on P/N interfaces, semiconductors, silicon chip etc.
Hey, that was my 200th post! The sign of a misspent life, surely.
That description of P/N switching is adequate considering that very few here know enough about the physics of semiconductors… a deeper explanation just isn’t possible. Semiconductor junctions can switch on & off much faster than any mechanical switch ever could. They are also free of problems like contact bounce and wear & tear that give mechanical switches a very short lifespan.
To my above description of how the multivibrator works, I should have added the three things required of any circuit which aspires to become an oscillator. The circuit must:
- consist of an amplifier which has gain
- receive properly synchronized feedback to encourage & sustain the oscillations
- have frequency determining components
Want to thank all once again for the responses.I have a pretty good idea now as to my question,which will be followed up with reading the suggested books/webpages.
I will move on now to some other questions that I have in a new post .Thanks again
ahem just a little point but electrons don’t actually circle around the nucleus.
Very true, but they do exist in clouds that are bound to the nucleus by magnetic forces. The Bohr model is commonly taught in elementary level classes simply because it gives a ‘good-enough’ idea of what the heck an atom is without making little brains explode from quantum physics.
Hopefully, the quantum model is taught later on. It explains so many neat things, like phosphorescence.
Someone said that the oscillators used in computers use quartz, which has a resonance. That doesn’t quite cut it, but comes close. Please see my extremely basic page dealing with quartz crystals at:
http://www.geocities.com/louis33772
For an excellent and very detailed explanation of quartz crystals and crystal controlled oscillators, follow the link I provide to Dr. John Vig’s tutorials.
A crystal controlled oscillator is a true marvel of design engineering used to exploit a natural occuring phenomena, namely piezoelectricity.