Effect on current, if a higher voltage is applied

Click For Summary

Discussion Overview

The discussion revolves around the relationship between voltage, current, and power in electrical circuits, particularly focusing on how changes in voltage affect current under different conditions. Participants explore the implications of Ohm's Law (V=IR) and the power equation (P=IV), examining scenarios where power is held constant versus when it is not.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants express confusion about the apparent contradiction between Ohm's Law and the power equation, noting that increasing voltage seems to imply both an increase and a decrease in current depending on the context.
  • It is proposed that if power is held constant, increasing voltage necessitates a decrease in current, highlighting the dependency on what variable is being held constant.
  • Others argue that in a resistive circuit, increasing voltage results in both increased current and power, emphasizing that one cannot change voltage while keeping both power and resistance constant.
  • A participant provides an example of a DC-DC converter, explaining that with a fixed output voltage, increasing input voltage leads to a decrease in input current while maintaining constant power.
  • Some contributions suggest that the equations are tools for understanding relationships rather than definitive statements of cause and effect, indicating that interpretations can vary based on the scenario.

Areas of Agreement / Disagreement

Participants generally do not reach a consensus, as multiple competing views remain regarding the relationship between voltage, current, and power under different conditions. The discussion reflects ongoing uncertainty and differing interpretations of the equations involved.

Contextual Notes

Participants note that the relationships between voltage, current, and power can vary significantly depending on whether power is constant or if other variables are held fixed, leading to different conclusions based on the specific context of the circuit being discussed.

Dalek1099
Messages
17
Reaction score
0
I'm confused over this because generally I'm told that if the voltage increases then so does current and this satisfies the equation:V=IR because I=V/R increasing the top of the fraction should mean that the current increases but this contradicts the equation:P=IV be=P/cause this time I=P/V and if you increase the voltage then the current should go down as is the rule with the bottom of the fraction.These two equations just don't make sense with each other-one equation says that increasing the voltage increases the current and the other says that increasing the voltage decreases the current.
 
Physics news on Phys.org
Dalek1099 said:
I'm confused over this because generally I'm told that if the voltage increases then so does current and this satisfies the equation:V=IR because I=V/R increasing the top of the fraction should mean that the current increases but this contradicts the equation:P=IV be=P/cause this time I=P/V and if you increase the voltage then the current should go down as is the rule with the bottom of the fraction.These two equations just don't make sense with each other-one equation says that increasing the voltage increases the current and the other says that increasing the voltage decreases the current.

Given a constant power, then increasing the voltage requires a drop in the current to maintain that constant power. It just depends on what you are trying to hold constant.

If you increase the voltage across a resistor, then both the current and power increase. V=IR and P=VI.
 
Dalek1099 said:
I'm confused over this because generally I'm told that if the voltage increases then so does current and this satisfies the equation:V=IR because I=V/R increasing the top of the fraction should mean that the current increases but this contradicts the equation: P=IV because this time I=P/V and if you increase the voltage then the current should go down as is the rule with the bottom of the fraction.These two equations just don't make sense with each other-one equation says that increasing the voltage increases the current and the other says that increasing the voltage decreases the current.

If you increase V, then I and P both increase. You can't hold P fixed when I and V are changing and R is being held constant.
 
As one concrete example, consider a high-efficiency DC-DC converter. The output voltage is fixed, and the output current through a resistor would be fairly constant. So the power drawn from the input terminals in this situation is pretty much a constant power Pin.

Now, as you raise the input voltage Vin, the input current Iin drops. It's a very common characteristic for DC-DC converters,
 
berkeman said:
Given a constant power, then increasing the voltage requires a drop in the current to maintain that constant power. It just depends on what you are trying to hold constant.

If you increase the voltage across a resistor, then both the current and power increase. V=IR and P=VI.

I think I get it now because you can't change one thing and keep 2 other things constant.
 
this time I=P/V and if you increase the voltage then the current should go down as is the rule with the bottom of the fraction.

What you have said is only true if P is constant. All three terms (P, I and V) are normally variables.

In most but not all circuits if you increase V then both I and P will also increase.

For a resistive circuit:

I = V/R
and
P = V2/R

By inspection it's clear that if you change V then P increases faster than I.
 
Dalek1099 said:
I'm confused over this because generally I'm told that if the voltage increases then so does current and this satisfies the equation:V=IR because I=V/R increasing the top of the fraction should mean that the current increases but this contradicts the equation:P=IV be=P/cause this time I=P/V and if you increase the voltage then the current should go down as is the rule with the bottom of the fraction.These two equations just don't make sense with each other-one equation says that increasing the voltage increases the current and the other says that increasing the voltage decreases the current.

The equations in Science are only ways of working things out. Like the rest of life, it's GIGO. Equations do not necessarily show which is cause and which is effect. You could probably have equally odd conclusions out of speed, time and acceleration equations if you were not so familiar with them.
 

Similar threads

Undergrad Does current decrease inside a wire or does it increase it's velocity?
  • · Replies 8 ·
Replies
8
Views
2K
High School Voltage & Current: Explaining the Basics for Beginners
  • · Replies 11 ·
Replies
11
Views
2K
High School Some Questions about Electric Current/Capacitors to help my understanding
  • · Replies 7 ·
Replies
7
Views
2K
Undergrad Which law defines the AC inducing voltage in the inductor?
  • · Replies 25 ·
Replies
25
Views
3K
Undergrad Capacitor connected to voltage source, vary plate separation
  • · Replies 9 ·
Replies
9
Views
2K
High School Found a circuit where current is zero across an ohmic device (dV>0)
  • · Replies 11 ·
Replies
11
Views
1K
High School Relationship between current and voltage.
  • · Replies 5 ·
Replies
5
Views
4K
High School Antenna induction, oscillating circuit generating EM Waves
  • · Replies 6 ·
Replies
6
Views
2K
Undergrad Let current from a Van de Graff generator flow through you
  • · Replies 5 ·
Replies
5
Views
4K
Undergrad Propagation of Errors, Ohm's Law
  • · Replies 6 ·
Replies
6
Views
5K