How do I interpret magnetic fields due to electric currents?

In summary, the student is confused on Magnetic Fields and is looking for help. The student understands the concept of an electric current producing a magnetic field, but is lost on how to interpret the formulas.
  • #1
mr_coffee
1,629
1
confused on Magnetic fields!

Hello everyone, we just started a chapter on magentic fields due to currents and I'm pretty lost. I'm looking at the homework and its making no sense to me..
I read the section and yet its not helping either. It gives lots of formulas but doesn't really explain how to interpret them. For instance:
Figure 29-25 shows four arrangements in which long parallel wires carry equal currents directly into or out of the page at the corners of identical squares. Rank the arrangements according to the magnitude of the net magnetic field at the center of the square, greatest first. (Use only the symbols > or =, for example a=b>c>d.)
http://www.webassign.net/hrw/hrw7_29-25.gif
I said:
a>d>b=c
which was wrong

How could u apparoach this? I understand if a current is going into the page and another current is going out of the page, u get a repulisve force, and if they are both going in the same direction, in or out of the page, u get an attractive force, but what's that mean about magntiude?

also:
http://www.webassign.net/hrw/hrw7_29-24.gif
i'm suppose to figure out:
f the net magnetic field due to the two currents is to be zero at point P, describe the current i2 in the right hand wire. (Select all that apply.)
into the page
out of the page
i2 > i1
i2 < i1
i2 = i1

I don't want the answers, I would like someoen to epxlain to me how to intrepert this, or can any of you direct me to a webpage that explains the rules? Thanks!
 
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  • #2
If the current goes out of the page then the field goes counter-clockwise around it, if it goes into the page the it goes around clockwise. So if we have a wire with a current going out. To it's right it would make a field going up and to it's left going down.
Now if there're two wires with currents in the same direction then the field in the middle of them is zero, since ,for example, the left wire makes a field that is going up in that position(to the right of the left one), and the right one makes a field going down and they cancel out. If their currents are in oppisite directions then the add to each other instead of cancelling out cause now they're going in the same direction.
With this you can easily solve the first question. It is obvious that the total field in the middle of a and b is 0 cause the bottom left will cancel out with the top right and the bottom right will cancel out with the top left.
 
  • #3
sorry i got lost... I understand the first part, when u said,
If the current goes out of the page then the field goes counter-clockwise around it, if it goes into the page the it goes around clockwise. So if we have a wire with a current going out.
but I'm lost when u said to its right it would make a field going up and to its left going down? U mean if you are going around in a counter clockwise position? to the right of the circle it would make a field going up and to its left going down? like 3 o'clock and 9?
 
  • #4
If the current comes out of the page, then at the 3 o'clock position
the B-Field is pointing from the bottom of the 3 toward the top of the 3.
At the 9 o'clock position, the B-Field points from the top of the 9 toward its bottom.
Usually we picture the B-Field as continuous loops. These "encircle" the current.

Electric current (moving electric charge) produces Magnetic Field.
the B-Field encircles the moving charge according to the right-hand-rule.
If you have a long straight wire, the strength of B decreases with distance
as 1/r ... specifically, B dot 2 pi r = mu I_enclosed .
(Different geometries of current-carrying wire have slightly different forms.)

Don't confuse Magnetic Field with the Force on moving charge BY the B-Field.
 
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FAQ: How do I interpret magnetic fields due to electric currents?

What is a magnetic field?

A magnetic field is a region in space where a magnetic force can be detected. It is created by the movement of electrically charged particles, such as electrons, and is typically represented by lines of force that indicate the direction of the magnetic force.

How are magnetic fields created?

Magnetic fields are created by the movement of electrically charged particles, such as electrons. This can occur naturally, such as in Earth's magnetic field, or can be artificially created using magnets or electric currents.

How do magnetic fields affect objects?

Magnetic fields can affect objects in different ways depending on the strength and direction of the field. They can attract or repel other magnets, influence the movement of electrically charged particles, and can be used to store and transfer energy.

What are some common applications of magnetic fields?

Magnetic fields have many practical applications in our daily lives. They are used in electric motors and generators, MRI machines, credit and debit cards, and even in compasses for navigation.

Can magnetic fields be harmful to humans?

In general, magnetic fields are not harmful to humans. However, exposure to extremely strong magnetic fields, such as those found in MRI machines, can cause temporary side effects such as dizziness or nausea. Long-term exposure to strong magnetic fields has not been proven to have any significant negative health effects.

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