# How do you determine the polarity rods placed in a solenoid?

• Nile Anderson
In summary, the question is about the steady-state condition, not the initial transient condition. Soft iron is ferromagnetic so it's magnetic domains line up with the applied magnetic field. At the end of the day, the flux goes through the iron in the same direction as it would if it were just air or a vacuum - but it flux density is much higher.
Nile Anderson
Now well the question is pretty straight forward , and please do not pass this by , I am in high school but I am a still a very accomplished physics student. I am currently doing Magnetism and I came by a question , where people are saying a solution that seems very
counter-intuitive to me.
Observe the image below :
https://scontent-atl1-1.xx.fbcdn.net/hphotos-xpt1/v/t34.0-12/11303617_1076701942357842_1492731568_n.jpg?oh=104c35896d5f63fc35c944b032598b97&oe=556DD2E5

Others are saying that D is the answer but I say that the answer is B. Now understand I am very open to suggestion, I mean what is a physicist without an open mind but my reasoning has kept leading me to B being the answer , now look at this , if we place these two materials in the Solenoid , in the way the current flows , we have a north on the right side based on the Right Hand Grip Rule . But here is where the division occurs , they believe that the north of the soft iron material is on the same side but I am saying that the iron material has to have the opposite polarity of the solenoid because that is how it normally works when something is magnetised. So I say the north of the Solenoid creates a south in the material on the right and vice versa. What do you think ? Is my answer a misconception ?

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When applying the right hand rule, the dotted lines indicate wires going behind the solenoid.
Letting your fingers follow the current (look at "I") up and behind will put your palm facing you and your thumb pointing to the right.
The iron material inside the solenoid will have the same polarity as the solenoid - otherwise iron-core electromagnets will not work.

Simon Bridge said:
When applying the right hand rule, the dotted lines indicate wires going behind the solenoid.
Letting your fingers follow the current (look at "I") up and behind will put your palm facing you and your thumb pointing to the right.
The iron material inside the solenoid will have the same polarity as the solenoid - otherwise iron-core electromagnets will not work.
But the flux does not initially travel through the iron cores
I am sorry but your answer is not elaborate enough for me

Nile Anderson said:
But the flux does not initially travel through the iron cores
I am sorry but your answer is not elaborate enough for me
Please I am familiar with magnetic circuits , feel free to explain making references to the one created here

But the flux does not initially travel through the iron cores
The question is about the steady-state condition, not the initial transient condition.
Transients can be arbitrarily complicated.

This is not a magnetic circuit question - soft iron is ferromagnetic so it's magnetic domains line up with the applied magnetic field.
see: http://hyperphysics.phy-astr.gsu.edu/hbase/solids/ferro.html

Nile Anderson
Simon Bridge said:
The question is about the steady-state condition, not the initial transient condition.
Transients can be arbitrarily complicated.
So what you are saying is at the end of the day , the flux travels through the iron just as how it would if air were there ?

Sort of - at the end of the day, the flux goes through the iron in the same direction as it would if it were just air or a vacuum - but it flux density is much higher.

Nile Anderson
Simon Bridge said:
Sort of - at the end of the day, the flux goes through the iron in the same direction as it would if it were just air or a vacuum - but it flux density is much higher.
Ah yes thank you , s I know because iron has much greater permeability than air , the flux density part, Ok so no matter how I take it , it only provides a path for the flux that already existed assuming of course that it itself was not already magnetised.

Nile Anderson said:
Ah yes thank you , s I know because iron has much greater permeability than air , the flux density part, Ok so no matter how I take it , it only provides a path for the flux that already existed assuming of course that it itself was not already magnetised.
Thank you, I made a rookie mistake in not examining holistically.

## 1. What is a solenoid?

A solenoid is a coil of wire that is used to create a magnetic field when an electric current passes through it.

## 2. How do you determine the polarity of the rods in a solenoid?

The polarity of the rods in a solenoid can be determined using the right-hand rule. If you point your right thumb in the direction of the current flow, the direction in which your fingers curl will indicate the north pole of the solenoid.

## 3. Why is it important to determine the polarity of the rods in a solenoid?

Knowing the polarity of the rods in a solenoid is important because it determines the direction of the magnetic field that is produced by the solenoid. This information is critical in many applications, such as in electromagnets and motors.

## 4. What factors affect the polarity of the rods in a solenoid?

The polarity of the rods in a solenoid is affected by the direction of the current flow, the number of turns in the coil, and the material used for the core of the solenoid. These factors can all impact the strength and direction of the magnetic field produced.

## 5. How can the polarity of the rods in a solenoid be reversed?

The polarity of the rods in a solenoid can be reversed by either reversing the direction of the current flow or by changing the orientation of the coil. For example, if the coil is flipped upside down, the north pole will become the south pole and vice versa.

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