AC FundamentalsBasic ConceptsBasic Electrical FundamentalsEE Questions / Answers

According to Ohm’s Law, Current increases, when Voltage increases,(I=V/R), But Current decreases, when Voltage increases according to (P=VI). Explain?

  If pressure (Voltage) increases,  current_________.
if your answer is ” also Increases”.
Then why we say that P = V x I, and V = P/I,
in other words V = 1/I
How can you explain This ?

Actually, according to Ohm,s Law I= V/R, clearly Current is directly proportional to the Voltage, But according to P=VI or I=P/V, it shows that current is inversely proportional to the Voltage.

Now Lets me try to explain this statement. 

It depends on how you increase the voltage if you increase it by keeping the power of the source constant or not,,
if the power of the source is constant then the current would decrease when voltage increasing  ….if you don’t care about the power and just simply replace the battery with a new one’s with higher power rating this can increase the current.

in Transformer, when voltage increases then current decrease because power remains constant…both side power is P=VI

By Ohm’s Law, Current (I) is directly proportional to the Voltage (V) if Resistance (R) and Temperature remain same. 
I = V/R…..or…R=V/I…..or……V=IR.

According to P=VI…or…I=P/V….or …V=P/I,….. It says that Current inversely proportional to the voltage if power remain same.
as we know that in Transformer, If power remain same, and voltage increase, then current decreases in Step Up Transformer. also Voltage decreases when current increases as in Step Down Transformer.

Also on the generation side, same story will be there if power is constant.
but if we improve the power, then current and Voltage both will be increase. 

So Do Not Confuse about this statement.

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Electrical Technology

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  1. anonymous says:


    1. Electrical Technology says:

      hmmm Nice,,,Welcome Dear

    1. Electrical Technology says:

      Welcome Dear

      1. manjunath says:

        yes I concluded that if power is constant then p=vi holds good , when power varies then ohm’s law as to be used is it correct.
        can u please explain how to keep power constant in generation side .
        suppose if power varies in generation side then what happens,will current increases with increase in voltage.Please explain I’m waiting for your reply.

        1. Electrical Technology says:

          This is for explanation purpose only… as we can take ideal case.. where the input power at generation side is equal to the the receiving end power (consider zero% losses).. the best example is Electrical Transformer where power is remain constant while current or voltage may step up or step down which depends on the transformer primary and Secondary winding design and position…

  2. High voltage = low amp<br /> Low voltage = high amp<br /><br />Is that correct?

    1. Electrical Technology says:

      In case of P = VI, When P is constant, then correct..<br />

  3. Rahul Bagri says:

    i do not completely agree, <br />for instance a 10hp motor running on 60% load is fed 415V, it will draw around 9A. If the same motor is fed 380V, it will draw 7-7.5A. So when motor is not running on full load capacity it will draw less current.

    1. Electrical Technology says:

      can you please provide formula for this calculation???? then we will explore the topic….

  4. Anonymous says:

    The current behave differently in coil of the heater and in a normal conductor. My point is what is the difference between the two conductor. The 12V system in the car glows a bulb and the same voltage produces heavy torque also through starter. PLEASE EXPLAIN! THANKS!

  5. Anonymous says:

    how to calculate power when we are applying ohms law.<br />

    1. Electrical Technology says:

      Not Ohm’s Law, but P =VI in DC Circuits,
      P = VI Cos fi …in single phase Ac Circuit
      and in three phase circuit
      P = 1.732 x V x I x Cos fi… where Cos fi = Power factor and 1.732 = Under the root 3

  6. Anonymous says:

    Awesome explanation. I had same question and was searching for its solution. Now I got it. Thanks.

  7. Anonymous says:

    thank for nice explanation.It means nothing would be changed if ohms Laws were never existed.

  8. Awsm explanation. I was having the same question and searching for solution. But after reading this every thing is clear to me. Please keep doing good deeds like this. Thanks a lot.

    1. Electrical Technology says:

      Thanks for appreciation… 🙂

  9. THANKS to the one who explained this article . was in little confusion . but now its clear . Thanks!!

  10. mohamood ameen says:

    ohm’s law is applicable at constant temperture.. current and voltage are directly proportional at constant temperature… but for variable temperature p= vi .. current and voltage are inverse… iis that correct admin.. waiting for reply..

  11. Krunal Patel says:

    Dear Sir can u please Explain which Type of Thyristors and Capacitors are used in Induction melting furnace?
    And Tell me why that type of used?

  12. This has been the most help I have found on the web, Thank you This cleared everything up.



  14. I agreee that if power is constant and then if voltage is increased then the current is decreased but if consider the resistance of wire carrying current then by ohm’s law current should be increased
    So how will explain thisthis?

  15. Thanks for explanation. I was also confused due to transformer.

  16. if the current in a circuit decreases the power dissipated by that circuit will ….. i need help

    1. Hari Patil says:

      if current decreases the power dissipated in circuit is decreases ,because power loss is I Squire R ,that’s why we are using high voltage transmission line for power transmission line .P=VI ,

  17. Hamza zafar says:

    if power is constant then p=vi holds good , when power varies then ohm’s law as to be used is it correct ??
    this is true?

  18. Anonymous says:

    Please give a example when and where ohm’s law is applicable?

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