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I hear people say things like "I only put 5 amps through the circuit but I put a bunch of volts". I don't understand how this is possible if V=IR. Lets say you have a circuit with 5 ohms of resistance so V=I(5). The amount of voltage and current I am allowed to put through it has to be proportional.

Can anyone can give a good intuitive answer (don't go too in depth with math) that is understandable?

Rhezner
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  • Transformers don't "just" exchange volts and amps. – Ignacio Vazquez-Abrams Jan 15 '16 at 05:32
  • Everything obeys **Maxwell's equations**, but these require calculus and vector math and are pretty complicated. So we use a simpler model called **lumped constant** where we assume resistors, voltage sources, etc. connected by ideal wires. For **DC** or steady-state circuits we also assume the voltage and currents are constant. This is where we use Ohm's law and KVL and KCL. But **transformers don't work at DC**, they require alternating current. AC analysis is more complicated; energy is still conserved but peak voltage and peak current may happen at different times. – MarkU Jan 15 '16 at 05:37
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    There are all kinds of circuits that are not resistors. Ohm's Law only applies to resistors and resistances. – Daniel Jan 15 '16 at 05:50
  • So are voltage and amperage always proportional in a DC circuit with resistance? – Rhezner Jan 15 '16 at 05:53
  • Voltage and current are always in the ratio of the resistance. If the resistance changes, then the ratio changes. There are devices with variable resistance - any wire for instance has a slight temperature coefficient of resistance - though thermistors have a much much greater variation. – Neil_UK Jan 15 '16 at 06:23
  • Ohm's law (V=IR) is only true for purely resistive elements of a circuit. There are many electrical components that are not ohmic in nature and do not obey ohm's law. – Robert Stiffler Jan 15 '16 at 11:36

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If you re-read your question, then it sort of answer's itself. Yes...in a pure DC circuit, Ohms Law is King, and so V=I*R. But you stated they said "I only put 5 Amps through the Circuit....so if they put a constant 5 Amps through the circuit, then the voltage will be the current times the resistance. Since they didn't state the Resistance, then the value of the Voltage may be a "bunch of Volts"....if the resistance is high enough. Simply put....under normal everyday simple DC circuits....most people drive them with either a Voltage or Current Source...but typically not both. If they drive the circuit with a Current, then they will see the Voltage go up proportionally. So I believe maybe they didn't mean they "Put In" both Current and Voltage, but they put in Current and Measured a Bunch of Voltage...or Vice Versa.

caldersm44
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  • I think I understand, I probably sound like an idiot but I love to understand things intuitively. Thanks for answering guys! – Rhezner Jan 15 '16 at 17:56