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Physics/How to apply the Ohm law ?


Hello Steve,

Here I am again, with an easy question. Here, we have 220 Volt output at the socket. Assume a transformer with a 1 Watt Power. The primary windings must have a resistance of 48400 ohm, am I right ?
So, the input voltage would be 220 Volt, current would be 0,0045 amper....Is this possible, while the R is very high, we may need a cable of many km's long ?

b- The output of the transformer is 1000 Volt, so the current at the secondary winding would be 1 mA, what happens when I connect a resistance of 100 ohm across the secondary windings of this transformer, the i must be the same, am I right, so the potential across the resistance would be 0,10 volt, am I right ? What happens with the 1000 volts ?

c- What happens when I connect a capacitor across the the secondary windings, would the potential difference be 1000 volts between the ends of the capacitor ?

With my best wishes,

No, that would be if all the power was dissipated by the resistance of the transformer alone.  That's a bad assumption, to say the least.  

So b- and c- are wrong to start with. Then there's the question of a capacitor, with an RLC circuit involved, and that's totally a different question.  You could reach far more than that with the right frequency, but no way could you reach that static.  I need you to ask me these questions in stages that help them make sense, so I can answer the second and third parts after the assumed part (the resistance of the first part, and therefore everything that follows) is totally wrong to begin with.  Please do this next time before making me read through the next bits.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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