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In other words could you just make a resistor valued at, say, 0.10 ohms, to generate the same amperage as a 1 ohm system running at 10 times the voltage? So why even play with higher voltages?

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- Thread starter mearvk
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- #1

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In other words could you just make a resistor valued at, say, 0.10 ohms, to generate the same amperage as a 1 ohm system running at 10 times the voltage? So why even play with higher voltages?

- #2

berkeman

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In other words could you just make a resistor valued at, say, 0.10 ohms, to generate the same amperage as a 1 ohm system running at 10 times the voltage? So why even play with higher voltages?

You generally use higher voltages to support higher powers, since the currents at low voltages can get large enough to require thick conductors (higher cost, weight, etc.).

Do you have specific examples in mind?

- #3

meBigGuy

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Say we had a 1K load and it requires 100ma (that's 10 watts) to do what we wanted it to do. We need 100V to get that current. As you said, If the resistence was 100 ohms, we would only need 10V to get 100ma, but that is only 1 Watt so the light wouldn't be as bright (or whatever), so we need to go up to 31.6V, which causes 316ma, for 10W.

If we want 10W with 10V we need to go down to 10ohms which is 1 amp. Now we need 10X bigger conductors or accept more power loss.

Power loss caused by high currents (proportional to the current squared) is the driving factor behind using 700KV or more in high power transmission lines.

Does that help?

- #4

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No, didn't have specific application in mind.

Thanks.

- #5

SteamKing

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http://en.wikipedia.org/wiki/Electric_power

Standard equipment in all basic courses on electricity.

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Derived from P = V * I = ( I * R ) * I = I^2*R so 10X current is 100X the watts loss in heat...

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- #9

meBigGuy

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The I^2 R dissipation of power is true regardless of what portion of the circuit you look at. Power adds linearly through the system.

The total system power may be dissipated as heat or any combination of work and heat (or sound, or light, etc). The heat and EM dissipation in wiring is generally assigned to the power loss category unless you are building a heater or an antenna (but that is arbitrary).

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