magnetic influention

[Function]

Hello

 

In my papers in preparation for the med school approval exam, there's an exercise I don't really understand: the professor who solved the exercise, failed to explain why the magnetic induction at the top of A is, as it is in the bottom, pointed in the plane of the paper (cross), same for B, and why it is pointed out of the paper under points C and D. (see drawing)

Asked is the point in which the magnetic induction is zero. I do understand that both conductors give the same magnitude of induction in C (which is the answer) but I don't get why the directions are opposed.

 

 

 

Could someone please clarify this to me?

 

Thanks.

 

Edited April 19, 2014 by Function

[studiot]

 

Could someone please clarify this to me?

 

 

Sorry you will need to explain your diagram a little further.

 

What are the continuous lines with 20A and 5A by them?

 

What sort of conductors do the cross and point represent?

Are they straight wires only or are they part of a loop?

And are they connected to each other?

[Function]

What are the continuous lines with 20A and 5A by them?

 

Those are straight conductors

 

 

What sort of conductors do the cross and point represent?

Are they straight wires only or are they part of a loop?

And are they connected to each other?

 

I don't think the cross and point represent conductors, but the sense of the magnetical induction field (don't know if that's the same as magnetic field)

 

Believe me, the diagram isn't clear to me, either! The professor just mentioned something about: here 'it' (whereof I assume she meant the sense of the magnetical field) points in the plane, here out of the plane, ...

 

What the page literally says:

 

"MAGNETIC FIELD AS A CONSEQUENCE OF A CURRENT-CARRYING WIRE

 

Magnetic field: [math]\left|\overrightarrow{B}\right|=\frac{\mu_0\cdot I}{2\pi r}[/math]

 

Unit magnetic field: [math]1\;T=1\frac{N}{Am}[/math]

 

[DRAWING OF THE RULE OF THE RIGHT HANDGRIP (relation sense B and I)]

 

[DIAGRAM]

 

The magnetic induction field is zero in

A

B

C

D"

Edited April 19, 2014 by Function

[studiot]

Here is what I think you your professor might be saying.

 

Two long straight parallel wires pass currents in opposite directions of 20amps and 5 amps.

 

Given the distances apart find the null points in the combined field.

 

Now the fields are additive and the field around a single wire is circular and inversely proportional to the diatance from it and given by the equation at the bottom of my sketch.

 

The sense of the fields is given by the right hand screw rule and is as shown.

 

This allows a section or plan to be drawn through any plane at right angles to the wires where the resultant field may be calculated.

 

Can you see how to do this?

 

Note the cross and point should really only be used for the current in the wires. (imagine looking at an arrow and seeing either the feathers or the tip)

Edited April 19, 2014 by studiot

[Function]

Oh dear, those are a lot of English scientifical words

I see how they are additive etc. and two inverse senses will cancel each other out, but do you have any idea what the meaning is of the crosses and the points under and above A, B, C and D?

Because I don't really believe those are conductors?

 

I'd say it has something to do with the distance from C and D to both the conductor with 20 A and the one with 5 A, but it doesn't make sense to me why the 'things', whether they are conductors or magnetic field lines, above and under C (and D) are opposite to each other?

 

Notice that, and I might've wanted to say this earlier, originally, only the 2 straight conductors, current and the dot line were given, not the crosses and dots! So this professor solved this exercise by putting these herself in this drawing. Why and how, however, is still not clear to me.

 

(& aren't your mistaken in the direction of the arrows in the magnetic field around your 5 A-conductor?)

Edited April 19, 2014 by Function

[studiot]

 

(& aren't your mistaken in the direction of the arrows in the magnetic field around your 5 A-conductor?)

 

According to your original sketch the 5A current is flowing in the opposite direction from the 20A current.

 

Therefore the magnetic field circles the wire in the opposite direction.

 

Note that you should not say "the 5A conductor"; rather say "the conductor carrying 5A", because both conductors could be identical, just one is carrying more current than the other.

[Function]

My physics teacher had explained to me why it is so, and now I understand it.

Here's the explanation:

 

[studiot]

It's good that you understand it now.

 

[Function]

Thanks for your help