Why is power volts * current?

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  • #26
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OOps serious transposition there. Should have been like this

P = Ie2 x R
and
P = Ee2/R

which shows the interdependency better by seeing both anyway.
 
  • #27
adjacent
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P = Ie2 x R
and
P = Ee2/R
What is e and E here? I guess e is ^.
What is E?
 
  • #28
sophiecentaur
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I don't have an intuitive understanding of this.
......
Thank you

I think you are asking too much to expect an intuitive understanding of this very formal idea if you are not familiar enough with the concepts involved. If you know the precise definitions of the variables involved then the relationship just naturally follows. This is where a bit of Maths gives the answer but a subjective view of what's happening cannot.
The Power delivered to a component relates to the rate at which charges are releasing their Energy - same as the power of a boiler is the rate at which lumps of coal are being burned. Saying that power should be the same as the flow of charge is like saying the boiler would produce the same power for the same number of lumps, whether they are lumps of coal, stone or ice. The voltage is the equivalent to the energy contained in each of those lumps (Joules per lump); it tells of the energy 'content' of each unit of charge (Joules per Coulomb). But the formulae say it all so much more concisely.
 
  • #29
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What is e and E here? I guess e is ^.
What is E?

My apologies for not continuing the definition of terms in the "repair" post but small "e" I'm using as "exponent" so Ie2 = I squared or current squared. "E", which refers to "electromotive force", is voltage. Specifically to keep terms clear

"P" is power in Watts (also often shown as W)
"I" is current in Amps
"E" is potential in Volts
"R" is resistance in Ohms
 
  • #30
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My apologies for not continuing the definition of terms in the "repair" post but small "e" I'm using as "exponent" so Ie2 = I squared or current squared. "E", which refers to "electromotive force", is voltage.

You can write either I2 or ##I^2## and it will be a lot clearer what you mean. (try quoting this post to see what I did, or look for the sticky down in the feedback section).
 
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  • #31
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You can write either I2 or ##I^2## and it will be a lot clearer what you mean. (try quoting this post to see what I did, or look for the sticky down in the feedback section).

Thank you. That is very helpful and I'm confidant it will make my future posts clearer, to myself as well as others..
 
  • #32
davenn
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and use V for voltage rather than E

E is more commonly use for Energy ... ie .... E = mc2

cheers
Dave
 
  • #33
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and use V for voltage rather than E

E is more commonly use for Energy ... ie .... E = mc2

cheers
Dave

That's actually curious. I was taught Ohms Law is I = E/R but I see now that textbooks and modern reference material replace E with V as you recommended. I may be old but not so old I can't change for something half way reasonable. V it is :)
 
  • #34
AlephZero
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The old name for "voltage" was "electromotive force", which is probably where enorbet's I = E/R came from.

The term EMF is still used sometimes (e.g. the "back EMF" in an electric motor) but being pedantic, the EMF is the "cause" of a voltage in a circuit, not the actual voltage itself. (And the name EMF is also confusing because it has nothing to do with the idea of "force" as used in mechanics.)

In the standard notation for electromagnetism E is the electric field, not the voltage. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/efromv.html
 
  • #35
sophiecentaur
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emf is still used when you are referring to an induced 'voltage'. So the secondary of a transformer has an 'emf' induced and an antenna will also have an emf induced into it and a chemical cell will generate an emf. This term distinguishes this manifestation of a voltage from the Potential Difference that is actually measured in a circuit, fed from a real electrical source - one with a source resistance (so called Internal Resistance of a battery)
So PD would be equal to Emf - Current times source resistance or:
PD=rI.
I remember my Dad always used E = IR, after his college ONC and HNC courses on 'EE' (=Voltage Voltage??haha). It confused me, wham I started using V = Ir at school.
Flavours change from generation to generation. I remember , in A Level Mechanics and Physics, acceleration was always lower case f. So v=ut+ft2/2 was what we used in our equations of motion calculation.
It's a moving target, as new variables arrive and pinch the commonly used symbols.
 

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