The title is enough
Look at the list of "Related Discussions" at the bottom of this thread, and you'll find two threads with the same question as yours. One of them has 24 responses, which looks promising!
Could you please copy and paste these links in a reply because the mobile version doesn't allow make these links appear
Thanks very much
unfortunately, I couldn't get much from related discussions, could you provide a thorough explanation,
thanks in advance
It's an experimental observation, first made in 1820. See http://inventors.about.com/od/lessonplans/ht/magnetic_fields.htm
The Biot-Savart law was inspired by this and other observations.
So you should be able to start with the Biot-Savart law, and get back to Oersted's observation.
It's simply due to the cylindrical symmetry of the system.
I know the observation, but I can't figure out its reason. Bio-Savarts law will only guide me to the direction of the field mathematically not logically nor intuitively.
How isn't it a physics question if I want a deeper answer??
Mathematics _is_ logic; and if you have a good intuition for geometry, you will do better with physical intuition as well.
Isn't there any other explanation, because bio-Savarts law is a way beyond my level b
What else than circular could it be? Do you expect rectangles? Why would you expect one direction from a straight wire look any different from other directions?
Why isn't there any poles
Why are the lines rotating around the wire and not ending or beginning at certain poles ?
"Why" questions in physics are always so ill-posed.
Can you answer that?
Because magnetic fields don't originate from "magnetic charges". Thus they always go in a loop.
You see this if you have some iron filings (in a sealed plastic box) - as you bring any magnet close the filings will form an alignment which connects the poles.
If you stick two magnets together, N-S or N-N, you will see changes in the alignment, but always in a closed loop.
If you "break" a magnet it will always have two poles.
One of Maxwell's equations describes this behavior, but you will need to study vector calculus to understand the math; at this point simply try to understand what you are seeing, and how it changes with the experiment.
For example, what do you expect the magnetic field to look like if you bend the current carrying wire into a loop? Into a long coil?
Here's an argument that the magnetic field around a straight wire has to be in circles simply because of the symmetry of the source:
Thanks a lot !!!!
Ampere Law states that
2[itex]\pi[/itex]r[itex]\Huge[/itex] [itex]\propto[/itex] [itex]I[/itex]
[itex]\beta[/itex] [itex]\propto[/itex] [itex]I[/itex]
2[itex]\pi[/itex]r[itex]\LARGE[/itex] is the maximum circumference for the field??
2πr is just the exact circumference of a circle with radius r.
There is nothing "maximal". The (theoretical, ideal) field extends to infinity.
That is a weird way to reduce Ampere's law.
What does it mean that circumference is directly proportional to the intensity ? Since there are infinite concentric circles
As I said, that is a weird way to reduce Ampere's law. You could read it "with larger current, you get the same field strength (which you omitted) at a larger radius".
And constant factors like 2π are irrelevant anyway if you look at proportional quantities.
I think Br [itex]\propto[/itex] [itex]I[/itex] seems more meaningful
their product is directly proportional to the intensity
how is B at the center of a circular loop and a solenoid derived from :
Ampere's circular law
B = [itex]\mu[/itex][itex]I[/itex] [itex]/[/itex] 2[itex]\pi[/itex]r
B at the center of a circular loop is similar to a circular line around a straight wire. Both can be calculated from the more general Biot-Savart law.
(which I found quickly via a Google search for "magnetic field at the center of a circular loop")
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