Voltage and current relation difference between Ohm's law and Power

bunny

Nov 4, 2015
3
Hi I am new to this forum According to Ohms law, at constant temperature voltage is directly proportonal to current.
But when we come to power formula p=vi which means that V is inversly proportional to I. How can we justify this?

Oct 14, 2014
111
Because resistance and power aren't the same thing.

bunny

Nov 4, 2015
3
Yar i know that both are not same but they relate same things no? and that to a law must be satisfied for all the things. We know that ohms law is valid only for ohmic conductors but power is same formula no?

Last edited by a moderator:

Oct 14, 2014
111
Yar i know that both are not same but they relate same things no?and that to a law must be satisfied for all the things.We know that ohms law is valid only for ohmic conductors but power is same formula no?
I'm not sure I understand the question. Here's an image that shows all of the different ways to relate power, voltage, current and resistance:

What do you believe isn't able to be justified?

AnalogKid

Jun 10, 2015
2,809
But when we come to power formula p=vi which means that V is inversly proportional to I. How can we justify this?

No, it doesn't. There is nothing to justify because your statement is incorrect.

For a constant resistance, voltage is directly proportional to current.
For a constant power, voltage is inversely proportional to current.

ak

Last edited:

duke37

Jan 9, 2011
5,364
To go one step further, P= V*V/R and P=I*I*R.
These can be derived from Ohms law by substitution.

Arouse1973

Dec 18, 2013
5,178
Hi I am new to this forum According to Ohms law, at constant temperature voltage is directly proportonal to current.
But when we come to power formula p=vi which means that V is inversly proportional to I. How can we justify this?
What do you mean justify?

Sep 18, 2015
452
Marshall Givens?

Ratch

Mar 10, 2013
1,098
Hi I am new to this forum According to Ohms law, at constant temperature voltage is directly proportonal to current.
But when we come to power formula p=vi which means that V is inversly proportional to I. How can we justify this?

First of all, Ohm's law is not V=I*R, and all its variations. Regardless of what predominates the electrical literature, a good physics book will tell you that Ohm's law is an electrical property of a material, specifically its electrical linearity. I can provide documentation for that statement if necessary.

So V=I*R is correct, but it is not Ohm's law. It is a definition. R is defined by the amount of current present at a specific voltage (R=V/I). Voltage is the electrical energy density of the charge (joules/coulomb). If V volts are lost to move Q coulombs of charge, then the energy expended is E=V*Q. Power is rate of energy and current is rate of charge. Dividing both sides of E=V*Q by t gives P=V*I.

Ratch

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