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Did you ever learn about "limits" or "asymptotes" in school? If you took the most basic algebra class, then you should be able to understand the idea behind this discussion.
Ohm's law when R = 0
- Thread starter screen1988
- Start date
As soon as you start talking about ideal hypothetical situations you risk entering a world in which intuition fails and you have to rely on the theory and the math. This often leads to confusion, but it can also lead to insights that carry over into the real world and yet better intuition.
Take this case. You ask how a current can flow if there is not voltage. The answer is, simple -- there is nothing that says that current can't flow without a voltage. But our everyday intuition tells us that this must be true. But it's just like a baseball that's been thrown. How can it keep moving toward the place once the pitcher is no longer forcing it forward? Simple. Newton's Laws don't require that you have to have a force to have motion, only that you have to have force in order to change motion. Same here. First, Ohm's Law isn't universal -- it only applies to the materials it applies to. Then consider an inductor -- how can you have a current when the voltage is zero? With a superconducting magnet, you have have hundred or thousands of amps running is a circle with no power and no connection to the outside world and it will be months or years before the parasitics will cause a noticeable reduction in current.
Take this case. You ask how a current can flow if there is not voltage. The answer is, simple -- there is nothing that says that current can't flow without a voltage. But our everyday intuition tells us that this must be true. But it's just like a baseball that's been thrown. How can it keep moving toward the place once the pitcher is no longer forcing it forward? Simple. Newton's Laws don't require that you have to have a force to have motion, only that you have to have force in order to change motion. Same here. First, Ohm's Law isn't universal -- it only applies to the materials it applies to. Then consider an inductor -- how can you have a current when the voltage is zero? With a superconducting magnet, you have have hundred or thousands of amps running is a circle with no power and no connection to the outside world and it will be months or years before the parasitics will cause a noticeable reduction in current.
djsfantasi
- Joined Apr 11, 2010
- 9,237
Here is a hoary joke from my younger days, that illustrates the concepts being discussed here, including limit theory, infinite/indeterminate values and the practical result.
In the college ballroom, all the girls in the class were lined up against one wall, and all the boys against the opposite wall. Then, every ten seconds, they walked toward each other until they were half the previous distance apart. A mathematician, a physicist, and an engineer were asked, "When will the girls and boys meet?"
The mathematician said: "Never."
The physicist said: "In an infinite amount of time."
The engineer said: "Well... in about two minutes, they'll be close enough for all practical purposes."
In the college ballroom, all the girls in the class were lined up against one wall, and all the boys against the opposite wall. Then, every ten seconds, they walked toward each other until they were half the previous distance apart. A mathematician, a physicist, and an engineer were asked, "When will the girls and boys meet?"
The mathematician said: "Never."
The physicist said: "In an infinite amount of time."
The engineer said: "Well... in about two minutes, they'll be close enough for all practical purposes."
