Is Voltage Directly or Inversely Proportional to Electricity?

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Discussion Overview

The discussion centers around the relationship between voltage and electricity, specifically examining whether voltage is directly or inversely proportional to current and power. Participants explore the implications of Ohm's Law and the power equation in different contexts, including theoretical and practical applications.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • Some participants assert that according to Ohm's Law (V=IR), voltage is directly proportional to current, while others point out that the power equation (P=VI) suggests an inverse relationship when considering constant power.
  • One participant clarifies that "electricity" should be interpreted as "current" in the context of Ohm's Law, emphasizing the distinction between resistance and power.
  • Another participant explains that increasing voltage while keeping resistance constant will increase current, which in turn increases power, potentially leading to overheating in devices not designed for higher currents.
  • Some participants discuss the implications of varying voltage and current while keeping power constant, noting that different devices behave differently under these conditions.
  • A participant introduces a hypothetical equation to illustrate how relationships can change based on underlying variables, suggesting that context matters in determining proportionality.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between voltage, current, and power, with no consensus reached on whether voltage is directly or inversely proportional to electricity. The discussion remains unresolved, with multiple competing interpretations presented.

Contextual Notes

Participants highlight the importance of understanding the definitions and contexts of the terms used, as well as the assumptions underlying the equations discussed. The discussion reflects varying levels of familiarity with the concepts, particularly among less experienced participants.

Who May Find This Useful

This discussion may be of interest to students learning about electrical principles, educators seeking to understand common misconceptions, and individuals curious about the relationships between voltage, current, and power in electrical circuits.

Elsa1234
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According Ohm's laws V=IR , which means voltage is directly proportional to electricity, but according to the formula of P=VI= V=P/I, voltage is inversely proportional to electricity, so what's wrong here?
 
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Elsa1234 said:
According Ohm's laws V=IR , which means voltage is directly proportional to electricity, but according to the formula of P=VI= V=P/I, voltage is inversely proportional to electricity, so what's wrong here?

You're comparing different things. And "electricity" doesn't come into V=IR , you mean "current". Ohms law tells you that the voltage is equal to current multiplied by resistance. So, if you increase the resistance, the current has to go down for constant voltage. V=P/I tells you that the voltage is equal to the power divided by current. So, if you increase the power, the current has to go up for constant voltage. Can you see that these are different things? Resistance and power aren't the same thing.
 
e.bar.goum said:
You're comparing different things. And "electricity" doesn't come into V=IR , you mean "current". Ohms law tells you that the voltage is equal to current multiplied by resistance. So, if you increase the resistance, the current has to go down for constant voltage. V=P/I tells you that the voltage is equal to the power divided by current. So, if you increase the power, the current has to go up for constant voltage. Can you see that these are different things? Resistance and power aren't the same thing.
Oh Yeah sorry, I meant current :p , you're explaining well, can you elaborate please? See I got the V=IR formula but V=P/I means that for the same power an electric appliance consumes, if you increease the current the voltage would decrease or vice-versa, how?
 
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Elsa1234 said:
Oh Yeah sorry, I meant current :p , you're explaining well, can you elaborate please?

I figured that's what you meant. :smile: I'd be happy to, but it might save us some time if you let me know what about the above explanation you didn't get.

In a physics sense, the Volt is equal to the potential difference between two parallel, infinite planes spaced 1 meter apart that create an electric field of 1 Newton per coulomb.

That is,

##V = \frac{Potential Energy}{Charge}##

It always helps me to think about units explicitly. In SI base units, V = 1 V = 1 kg·m2·s−3·A−1. If you shuffle around the units of the equations you quoted, you'll find that they all give the same definition of V.

Or, by Ohms law and Joules law, we know that

##V = I * R = \frac{P}{I}##

In SI units,

##V = A * \Omega = \frac{W}{A}##

And if you juggle the units a bit, you quickly see that##V = A * \Omega = \frac{W}{A} = \frac{J}{C}##
 
e.bar.goum said:
I figured that's what you meant. :smile: I'd be happy to, but it might save us some time if you let me know what about the above explanation you didn't get.

In a physics sense, the Volt is equal to the potential difference between two parallel, infinite planes spaced 1 meter apart that create an electric field of 1 Newton per coulomb.

That is,

##V = \frac{Potential Energy}{Charge}##

It always helps me to think about units explicitly. In SI base units, V = 1 V = 1 kg·m2·s−3·A−1. If you shuffle around the units of the equations you quoted, you'll find that they all give the same definition of V.

Or, by Ohms law and Joules law, we know that

##V = I * R = \frac{P}{I}##

In SI units,

##V = A * \Omega = \frac{W}{A}##

And if you juggle the units a bit, you quickly see that##V = A * \Omega = \frac{W}{A} = \frac{J}{C}##

See I got the V=IR formula but V=P/I means that for the same power an electric appliance consumes, if you increease the current the voltage would decrease or vice-versa, how? I'm a grade 8 student, I don't clearly get the facts but I'm curious , so could you explain me by giving examples? :)
 
Elsa1234 said:
See I got the V=IR formula but V=P/I means that for the same power an electric appliance consumes, if you increease the current the voltage would decrease or vice-versa, how? I'm a grade 8 student, I don't clearly get the facts but I'm curious , so could you explain me by giving examples? :)

The two formulas are used for different things. Ohm's law shows a relationship between voltage, current, and resistance.
The other equation is used to show the relationship between power consumed, voltage, and current.

If I have a circuit and I measure a voltage of 10 volts and a current of 1 amp, then I know that the resistance of the circuit must be 10 ohms since R = V/I and 10/1 = 10.

That same circuit will be consuming 10 watts of power, which follows from the power equation P = IV: P = 1*10 = 10 watts

If I increase the voltage to 20 volts, then the circuit now has 2 amps running through it since: I = V/R, I = 20/10 = 2 amps

Since both the voltage and the current has increased, the new power consumed is: P = 2*20 = 40 watts.

Note that I never changed the resistance in the circuit, only the voltage. I could change the resistance, which will change the amount of current flow and the change in current flow will change the amount of power consumed, per the equations.
 
Elsa1234 said:
See I got the V=IR formula but V=P/I means that for the same power an electric appliance consumes, if you increase the current the voltage would decrease or vice-versa, how? I'm a grade 8 student, I don't clearly get the facts but I'm curious , so could you explain me by giving examples? :)

You should read ##V=P/I## to say that you can get the same amount of power out of the appliance if you double the voltage and halve the current. However, you have to remember that the current is still determined by the resistance (##V=IR##), so if you just double the voltage without changing the resistance, you'll get twice the current and twice the power (and your appliance will catch on fire because its wiring can't handle the increased current). Thus, if you're going to do something to change the voltage while keeping the power constant, you have to also do something to change the resistance so that the current changes too.

An example:
The table saw in my basement is powered by a 1.5 horsepower electric motor - that's the power output given by ##P=IV##. Inside the motor there are connections that can be configured to change the resistance of the motor windings so that the motor produces that 1.5 HP using either 20 amperes and 120 volts or 10 amperes and 240 volts - convenient, because those are the two voltage levels widely available in North America.
 
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Elsa1234 said:
According Ohm's laws V=IR , which means voltage is directly proportional to electricity, but according to the formula of P=VI= V=P/I, voltage is inversely proportional to electricity, so what's wrong here?
Use those two equations to find the relationship between P and R in terms of I and V.
 
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Elsa1234 said:
See I got the V=IR formula but V=P/I means that for the same power an electric appliance consumes, if you increease the current the voltage would decrease or vice-versa, how? I'm a grade 8 student, I don't clearly get the facts but I'm curious , so could you explain me by giving examples? :)
For some devices you can hold power constant when varying voltage (motors), but for others (resistors) you can't, so you need to know which equation to apply in which situation. Generally, you can hold other things constant and vary the current.
 
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Elsa1234 said:
According Ohm's laws V=IR , which means voltage is directly proportional to electricity, but according to the formula of P=VI= V=P/I, voltage is inversely proportional to electricity, so what's wrong here?

As others have said. The short answer is that P isn't a constant. It's also dependent on the current. Your problem is actually nothing to do with Ohms law and electricity...

Take any old equation such as this one that I just made up...

A = B/C

At first glance it looks like A is inversely proportional to C.

But If I then told you that B = C2 you would get a different answer. By substituting you get..

A = C2/C = C

So A is directly proportional to C.
 
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