Another curious question -- Why is current proportional to voltage?

1. Aug 22, 2014

Hi guys I just want to know why is the current directly proportional to the voltage is that because voltage increase the speed of electrons?? or ,just increase the number of electrons?????

2. Aug 22, 2014

And what does it mean when we say high or low potential

3. Aug 22, 2014

analogdesign

Current is only directly proportional to voltage in materials that obey Ohm's law.

You can look at it from a few standpoints. charge/time is the definition of a current. V = IR in an Ohmic material so you could say V is the required pressure to push I electrons/time through a resistor of resistance R.

Potential is another word for voltage. So high potential is high voltage. You can think of it as kind of an analogy to high pressure or high potential energy. If you put a large potential across a small resistor you'll get a large current. ( I = V/R)

4. Aug 25, 2014

mr_pavlo

In each type of conductor there is an certain amount of free electrons. These electrons are permanently moving due to thermal energy. This happens also without electric field applied and it is random movement so overall current is zero. But when you apply some amount of external electric field then this movement of electrons begins to predominate in the direction of this field so the current starts to flow. So the number of electrons is always the same. The voltage only makes their random movement less random. And for beter conception thermal velocity is the order of 100000 meters/sec but the velocity caused by electric field is something like centimeters per hour.

5. Aug 25, 2014

So you mean when the voltage is high it creates stronger electric field and more electrons predominate in the direction of the field and more electrons mean more current right !??!!

6. Aug 25, 2014

gerbi

Voltage is calculated as difference between potentials. Do not confuse these terms.

7. Aug 25, 2014

sophiecentaur

Field is the gradient of Potential* so, yes: The field is what causes the electrons to drift more in one direction than another.

*Volts per metre

8. Aug 25, 2014

analogdesign

This may be true in physics, but in electrical engineering the terms are used interchangeably. If you insist on distinct definitions you will be very confused by a lot of the EE literature and circuit design lore.

9. Aug 25, 2014

sophiecentaur

Hmm. I know that a Voltmeter is never called a PD meter but I don't think there's much opportunity for confusion if you start from the definitions and use them properly. There is a lot of engineering slang that gets in the way of proper understanding of a lot of EE. Terms like "Amperage" and 'Current Draw', for instance, come in from a practical side of things which is hardly even 'Engineering', with a capital E. "Lore" is not the best source of informed knowledge, if you want to get things right and it can be a struggle if someone has only that sort of knowledge available. A certain amount of 'unlearning' is often necessary, to make the transition from acquaintance to a serious understanding.
At least there is PF; available for nearly everyone in the World, these days. A bit fussy and pedantic at times, perhaps, but a good rock to anchor your EE learning to.

10. Aug 25, 2014

analogdesign

That's a fair point. Although, for a lot of the more advanced areas of endeavor there isn't much available beyond lore.