# Recent content by Dmytry

1. ### Why is the Norelco 1.1kW step-down device so compact?

What does it do? Is it stepping down 240v AC to 120v AC ? Is it outputting DC? I've opened some step down device of the former kind, it just had an SCR, a small-ish inductor, and a few other parts - basically, pre-set dimmer circuit. Really nasty.
2. ### What's in an electronics hobbyist's toolbox?

Ya. Can't stress it enough - measure the stuff, sometimes something gets mis marked. I got resistor kit in pieces of tape (as for feeding into machine), 50 values each with 50 resistors, and I measured one each value and wrote it on tape itself. I still can't quickly read the colour codes...
3. ### Current through voltage doublers

if you are discussing the doubling rectifier such as bridge (Delon) doubler http://en.wikipedia.org/wiki/Voltage_doubler then the maximum current depends on the value of capacitors, and indeed the current through load will be half of the current that flows from AC source into the doubler as...
4. ### How Transistor works - verifying

Well the point of education is twofold: teach everyone to read and write and do very basic math, and get started those who will become professionals in complicated fields (who will be few). It would seem to me that west often neglects the second goal nowadays or sacrifices it for the first...
5. ### How Transistor works - verifying

Well, I seen it as a real circuit element. Also, that model is not so bad. It is a common explanation that minority carriers in the base region are responsible for conduction. Of course it does breed misconception with two diodes for some people but I don't recall ever thinking that I can...
6. ### How to think about ground planes

Well the small cap should be covering the highest frequencies best unless it is too far or otherwise has too much inductance. Basically, suppose you got two planes, like, a planar capacitor. One is ground plane other is vcc plane. Charged to some voltage. If you short the ground plane and vcc...
7. ### How Transistor works - verifying

I recall reading how BJT works in an old book when i was about that age. It was explained that it would normally not pass any current, as two diodes would not, but as the base is so thin, injection of other type of charge carriers into the base by making one of diodes conduct current makes the...
8. ### Why DC is said to be more dangerous than AC?

It's Edison's war of currents backfiring. The way I heard of this is that muscles are controlled with pulses sent through nerves repeatedly (with AC), and the AC has similar frequency and is thus more effective at making you hold onto the wires. The nervous system generally sends a...
9. ### Very confused about path of light from distant galaxies :-(

except in 250 M years, the light was not 250M light years away from you, but much further, because the space expanded during that 250M years. It's like a bug crawling at constant speed on the rubber sheet that is being stretched. You're correct though that simple moving away wouldn't make it...
10. ### Time Dilation and Length Contraction the same thing?

Both are results of how Lorentz transformation work. It's pointless to ask for verbal descriptions; you should look up the Lorentz transformations; those equations tell of how it works; you need to learn to read the equations as there is no satisfactory no-math verbal dissection of that whole...
11. ### Why are the effects of Time Dilation permanent but Length Contraction is Not?

The twin that returns, however, will - upon return - be aging at the same rate as the twin that stayed home. The clock that the twin took with him in a voyage will be counting off time length of 1 second, in a second, when he's back home. The length of the travelling twin's sleep, or the length...
12. ### How to think about ground planes

Well, that would depend to how the current (that is being injected) is supplied. In general, yes, you can have ripples in the ground and power planes, yes they travel like waves in the pond, and yes, they can get into the analog side, and yes you are better off separating the analog power and...
13. ### Real-life NOT Gate?

That's a joke. It's when you have nothing connected to the memory bus. You can do writes, but you can't read anything out. A pun on the read-only memory which can only be read but not written, the write-only memory can only be written to, but not read. Sometimes external devices function as...
14. ### Sinc function in nature?

Sort of, though I wouldn't describe it this way. The intensity is given as integral of the phase from the slit to the screen over the slit width. When you are calculating intensity of the light in direction a (in radians off the centre) you're summing the contributions from every point on the...
15. ### Sinc function in nature?

Hmm, off top of the head if you shine light through a slit it should diffract like sinc function (the amplitude being sinc function squared) for exact same reason why fourier transform of aperiodic square is sinc.