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Question:

Describe what will happen to two solenoids that are arranged next to each other as shown. The solenoids are the same length, and have the same number of turns and current flowing through them. Explain your reasoning.

enter image description here

Using the right hand grip rule for solenoid, that is, curled fingers represent the conventional current and the thumb represent the magnetic field, I concluded that the magnetic field points downwards for both of them. Subsequently, this means that they attract.

But the answer gives that the solenoids will repel.......

So where is my misconception? I believed I used to correct rule and applied it correctly too.

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A. the magnetic field inside the solenoids is down, but out of them is up. (That's your mistake, if you remember that everything becomes correct :) )

B. Some intuition for knowing which result you should be expecting: you can think about each solenoid like a bar magnet with its north pointing down and south pointing up (think about the field lines, they emerge from the down direction and come back to the upper part of the solenoid, just like a bar magnet with its north pointing downward). If you arrange two bar magnets with their poles arranged that north is next to north and south next to south, you will get repulsion

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  • $\begingroup$ Thanks Sir, I am not sure what the following sentence means: "the magnetic field inside the solenoids is down, but out of them is up". I am unsure what you are referring to $\endgroup$
    – Probability_Sarah
    Commented Aug 11, 2020 at 8:04
  • $\begingroup$ My book says that if the conventional current travels the same direction in the 2 solenoids, they will attract. Isn't this question an example of this? $\endgroup$
    – Probability_Sarah
    Commented Aug 11, 2020 at 8:05
  • $\begingroup$ @Negrawh notice the picture here: i.ytimg.com/vi/xHRlpooUCqM/maxresdefault.jpg in and out of the solenoid the field has opposite directions $\endgroup$
    – Ofek Gillon
    Commented Aug 11, 2020 at 11:57
  • $\begingroup$ Your first statement is incorrect. Both magnetic fields are emerging from the lower ends. Your last statement is correct. $\endgroup$
    – R.W. Bird
    Commented Aug 11, 2020 at 18:52

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