Magnetic field dependent on current only....

Discussion in 'Misc Electronics' started by qude, Jun 19, 2005.

1. qudeGuest

right?

This means the 12volts/18ampere setup produce larger
magnetic field magnitude (from the current flow) than
the 110volts/2Ampere setup (noting that both produce the
same 220 Watts power), right??

Or does the larger 110 volts in the latter give more push
to the 2 ampere resulting in similar magnetic field
magnitude for both setups??

If the answer is that the 12volts/18 ampere indeed
produce larger magnetic field, do designers find it
necessary to use larger voltage instead of larger
current to prevent magnetic field interference?

If the answer is that both produce the same magnetic
field magnitude, then it means in larger voltage
such as 110 volts, it pushes the 2 ampere more so
it moves faster compared to the 18Ampere with 12
volts that don't push it faster. If not, how can
the magnetic field magnitude in both be the same
(assuming they are the same).

Thanks.

qude

2. redbellyGuest

The 18 amp wire will have a larger magnetic field, at least in the
vicinity of the wire. It is further complicated because the wires are
usually coiled or double-coiled, and the geometry of the lead wires
could have an effect as well.

HOWEVER: magnetic fields are of no consideration whatsoever in light
bulb design. Designers use the voltage source that is available: if
the bulb is to be used in a household in the USA, this is 110-120 V.
If for a household in most other countries, it is 220 V (or somewhere
thereabouts). If it's for a car, then 12 V.

3. sue jahnGuest

Correct!
<< In conclusion, ***all*** magnetic fields encountered in
nature are generated by circulating currents. There is no fundamental
difference between the fields generated by permanent magnets
and those generated by currents flowing around conventional
electric circuits. In the former case the currents which generate
the fields circulate on the atomic scale whereas, in the latter case
the currents circulate on a macroscopic scale
(i.e., the scale of the circuit). >>
http://farside.ph.utexas.edu/teaching/302l/lectures/node62.html

No. Fewer charges need to move past a point in
a second to transfer the same energy because they are
moving faster. Tho' charges have energy, (angular momentum)
it is not created nor destroyed. The energy that does
the work is the mass(equivalent energy) of the charge in motion.
Hmmm... Frequently higher voltages are used to avoid
thick wire. I can't think of an example. There are other
techniques that are more effective, but in principle you
are correct.
But it isn't. You got it right above.

Sue...

that both produce the same magnetic

4. Don KellyGuest

--
Don Kelly

---------
Who were you answering? There is no indication of what you are saying
"right" to. Please include at least some of the material you are responding
to.

The magnetic flux density due to a wire carrying current I is proportional
to the current and inversely proportional to distance. The presence of other
current carrying wires (such as the necessary return path(s) affect the flux
density so consideration of a single wire in space is not a realistic
option(effectively you have a single turn coil with a return conductor
infinitely far away).
The field due to a current of 2A is 1/9 that due to a current of 18A at a
point external to the wire.

Is this of importance to decisions as to what voltage is to be used? Not
really.

There is an optimum voltage level depending on the power to be transferred
and the distance it is to be transferred (at a given frequency). Rule of
thumb- more power and or longer distance- go to higher voltage. This is not
a physical rule- but an economic one. That is why AC transmission put
Edison's DC systems out of business. You can transmit 100MW at 200V for a
distance of 200 miles but the cost would be horrendous compared to doing it
at 140,000V. However, to use 140,000 V to supply a home would be rather
dangerous, expensive, and ridiculous so 120/240 is a good practical and
economic balance. (Sue, you should know this- examples are all around )

5. redbellyGuest

He was saying "right?" to the header of this thread, "Magnetic field
dependent on current only...."