Current Induced in one circuit by another circuit

[sciencec]

Homework Statement

Hello! I have a question regarding an induction exercise. It says “The current induced on the right side circuit by the left circuit after closing the interruptor is.....”
a. clockwise
b. counterclockwise
c. other

I would appreciate any help. There is no additional data given.

Relevant Equations

Faraday-Lentz Laws

 

[cnh1995]

As per forum rules, you need to show your work to receive help.
Fill the "Attempt at a Solution" section of the HW template.

 

[Delta2]

I think you need to tell us if both the coils are identical, or at least if they have the same clockwise or counter clockwise rounding of the wire.

Also if the magnetic field of each coil is totally confined in the interior of the coil (which practically is the case) or some of it escapes in the environment (which is the theoretical case).

And finally if the self inductance of each circuit(minus the inductance of the coil) is negligible or not.

 

[Merlin3189]

Since this is a purely qualitative question, Lenz's law is all you need.

AFAIK there are no coils, just bits of wire. No matter how long or how close, their magnetic fields interact. No numbers are asked for, so however small the effect, you just need to decide which way the current flows.

 

[sciencec]

I think you need to tell us if both the coils are identical, or at least if they have the same clockwise or counter clockwise rounding of the wire.

Also if the magnetic field of each coil is totally confined in the interior of the coil (which practically is the case) or some of it escapes in the environment (which is the theoretical case).

And finally if the self inductance of each circuit(minus the inductance of the coil) is negligible or not.

they are both identical coils from what I can understand. I’m guessing in this case the field from the left coil does escape, which in turn will cause the right coil to have a field. my question is, that field will be in which direction? Inwards, therefore having a clockwise moving current? Or outwards, therefore having a counterclockwise moving current?

 

[sciencec]

Since this is a purely qualitative question, Lenz's law is all you need.

AFAIK there are no coils, just bits of wire. No matter how long or how close, their magnetic fields interact. No numbers are asked for, so however small the effect, you just need to decide which way the current flows.

Is there a specific way the current flows? I know the current on the left side is moving counterclockwise causing an “outwards” magnetic field. So does the second circuit establish a current in that same direction, or in the opposite direction? My profesor never explained this topic but says an exercise related to this will appear in the test.

 

[cnh1995]

moving counterclockwise causing an “outwards” magnetic field

That magnetic field will "link" with the right side circuit. In which direction?

 

[sciencec]

That magnetic field will "link" with the right side circuit. In which direction?

That’s what confuses me. Do I take Lentz law into consideration? If I do then the current on the right side circuit will love clockwise. If Lentz Law does not apply then the current would be the same as the inducing current.

 

[cnh1995]

If I do then the current on the right side circuit will love clockwise.

Magnetic field due to a current carrying conductor "encircles" the conductor.

So, when the switch is closed in the left circuit, which way will the magnetic field be in the right side circuit?

 

[sciencec]

Magnetic field due to a current carrying conductor "encircles" the conductor.

So, when the switch is closed in the left circuit, which way will the magnetic field be in the right side circuit?

clockwise?

 

[cnh1995]

clockwise

I asked magnetic field direction, not the current direction.

Can you draw the magnetic field lines formed by the current in the left side circuit?
Hints: 1) Magnetic field will be perpendicular to the plane of the screen.
2)Magnetic field due to a current carrying conductor "encircles" the conductor.

 

[sciencec]

I asked magnetic field direction, not the current direction.

Can you draw the magnetic field lines formed by the current in the left side circuit?
Hints: 1) Magnetic field will be perpendicular to the plane of the screen.
2)Magnetic field due to a current carrying conductor "encircles" the conductor.

Oh right sorry English isn’t my first language.

 

[Delta2]

Since this is a purely qualitative question, Lenz's law is all you need.

AFAIK there are no coils, just bits of wire. No matter how long or how close, their magnetic fields interact. No numbers are asked for, so however small the effect, you just need to decide which way the current flows.

So in your approach you consider that the two inductors do not interact (not sure what you mean there are no coils, each circuit has an inductor connected), and only the connecting wires of the two circuits interact with their magnetic fields. Am I correct so far?

 

[sciencec]

If anybody can please tell me which way the current moves in the right circuit i would appreciate it greatly. This exercise is not part of homework, it is just a practice exercise given to me from one of the students in my class. It does not count towards a grade. Since this topic is coming in the test, I would like to understand the problem well. My professor does not like answering students questions so I have no where to turn to. So if anybody could tell me what direction the current would be I would figure it out from there. I understand that the counterclockwise current in the left produces an outwards magnetic field. I’m just confused regarding wether the induced current on the other side would be also counterclockwise or clockwise. Please understand that i’m learning this topic in spanish, therefore it is a hard for me to understand the concepts themselves in english. I appreciate the help

 

[cnh1995]

Oh right sorry English isn’t my first language.

As far as geometry is concerned, you have correctly drawn the magnetic field.
You also correctly said the field is "outward" in the left loop. So the field "linking" with the right side is in which direction?

 

[sciencec]

As far as geometry is concerned, you have correctly drawn the magnetic field.
You also correctly said the field is "outward" in the left loop. So the field "linking" with the right side is in which direction?

inwards.

 

[cnh1995]

inwards.

Yes.
So the right loop saw a sudden "increase" in the magnetic field "inwards" (into the plane of the screen). How will the right loop react to this change?

 

[sciencec]

Yes.
So the right loop saw a sudden "increase" in the magnetic field "inwards" (into the plane of the screen). How will the right loop react to this change?

It will react to the increase in inwards magnetic field by “creating” (don’t know what word to use) an outwards field to counteract, meaning the current will be counterclockwise.

 

[cnh1995]

It will react to the increase in inwards magnetic field by “creating” (don’t know what word to use) an outwards field to counteract, meaning the current will be counterclockwise.

Yes.

But I beileve this problem is poorly framed.
1) The two circuits are drawn with lumped circuit abstraction, which means there should be no fields and the geometry of the two circuits won't matter.
2) If the problem-setter wanted to demonstrate Lenz law through this example, it would be better to use coils instead of resistor loops IMO. Then it will no longer be lumped element abstraction and you can analyse it using fields. (If the lumped element abstraction is considered in this circuit, there is no magnetic coupling between the two coils. So, no induced emf and induced current.)
Maybe I'm being pedantic here, but if I were to set this problem, I would use coils instead of lumped resistor loops.

 

[sciencec]

Yes.

But I beileve this problem is poorly framed.
1) The two circuits are drawn with lumped circuit abstraction, which means there should be no fields and the geometry of the two circuits won't matter.
2) If the problem-setter wanted to demonstrate Lenz law through this example, it would be better to use coils instead of resistor loops IMO. Then it will no longer be lumped element abstraction and you can analyse it using fields. (If the lumped element abstraction is considered in this circuit, there is no magnetic coupling between the two coils. So, no induced emf and induced current.)
Maybe I'm being pedantic here, but if I were to set this problem, I would use coils instead of lumped resistor loops.

I agree with that. I was also confused when i saw the problem initially because of the use of resistor loops instead of coils. Aside from that, thank you very much for taking your time and helping me i greatly appreciate it.

 

[Delta2]

LOL guys, are those two lumped elements in the pictures , representing a resistor or an inductor? I thought it was an inductor lol...

 

[cnh1995]

They look like resistors to me ;)
If they were inductors, their winding directions need to be given, as you said in #3.

 

[Merlin3189]

I don't know where the zig zag lines are inductors, but perhaps they are somewhere?
I took them as resistors and the induction was due to the parallel wires.
If they are inductors, there ought to be some indication of the sense of the windings. Also there should be some indication of coupling. As someone mentioned, if they are purely schematic, so that you can't assume those two wires are parallel, then equally you shouldn't assume the coils are coupled.

 

[Delta2]

My bad, I think @Delta2 's demon tricked my mind and made me see inductors there while they are resistors .

 

[rude man]

They look like resistors to me ;)
If they were inductors, their winding directions need to be given, as you said in #3.

Only if mutual inductance between the two "coils" is assumed.

If the mutual inductance is between the wires only, which is the case if they're resistors, then the direction of winding of the coils would be immaterial.