Physics Solenoid concept

[DiamondBar]

The book says "magnetic field will be stronger if the current is increased or if we are positioned CLOSER to the wire." However, a few pages later on when we get to solenoids, this is the opposite?

"Magnetic field's maximum magnitude is on the central of the coil, and it gets weaker as we move away from the center to the coils."

But the same equation seems to prove otherwise:

B= I/r

B is the magnetic field
I is the current
r is the radius


I dont get why B in solenoids get stronger as you move AWAY from the coil to the center. Please help!

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[BerkReviewTeach]

The book says "magnetic field will be stronger if the current is increased or if we are positioned CLOSER to the wire." However, a few pages later on when we get to solenoids, this is the opposite?

"Magnetic field's maximum magnitude is on the central of the coil, and it gets weaker as we move away from the center to the coils."

But the same equation seems to prove otherwise:

B= I/r

B is the magnetic field
I is the current
r is the radius


I dont get why B in solenoids get stronger as you move AWAY from the coil to the center. Please help!

If you look at Figure 8-17 on page 136, that should help. Note that moving away from the absolute center point of the solenoid (defined by 0 on the graph) to either the left or the right shows a drop in the magnitude of the B field. This is because you are getting farther away from the loops at one end of the solenoid, and their impact is reduced.

If you were to number the loops in the solenoid 1-41, then when you are in the middle of loop #21, you feel a strong field from 21, semi-strong from 20 and 22, kind of strong from 19 and 23, and so on down to feeling 1 and 41. However, when you move to say the left down to the middle of loop #11, then it's a case of 11, 10/12, 9/13, and so on, but 21-41 will have a much smaller impact overall than they did when you were in the middle of loop #21. This explanation really helps if you can match it to the picture in Figure 8-17.

Have you done the passages for section 8 yet? That will help a great deal with this concept.

 

[DiamondBar]

If you look at Figure 8-17 on page 136, that should help. Note that moving away from the absolute center point of the solenoid (defined by 0 on the graph) to either the left or the right shows a drop in the magnitude of the B field. This is because you are getting farther away from the loops at one end of the solenoid, and their impact is reduced.

If you were to number the loops in the solenoid 1-41, then when you are in the middle of loop #21, you feel a strong field from 21, semi-strong from 20 and 22, kind of strong from 19 and 23, and so on down to feeling 1 and 41. However, when you move to say the left down to the middle of loop #11, then it's a case of 11, 10/12, 9/13, and so on, but 21-41 will have a much smaller impact overall than they did when you were in the middle of loop #21. This explanation really helps if you can match it to the picture in Figure 8-17.

Have you done the passages for section 8 yet? That will help a great deal with this concept.

OHHHHHHHHHHHHHHH
I was imagining the "center of the solenoid" being the center of the circle (cross sectional view)



( - ) <- if ( and ) represent the circle, the middle of the circle, the center.


I didnt know it meant center as in


(((((((((((((((((((((((((((((((( )

^ being this midpoint of the view of the solenoid from the side


LOLL!! Thank you so much for clearing this up!
if you see any flaws to what i've just posted, feel free to point it out, but everything is clear to me now! (I hope)



as for the pages and figure and example #s, I am using princeton review

 

[BerkReviewTeach]

OHHHHHHHHHHHHHHH
I was imagining the "center of the solenoid" being the center of the circle (cross sectional view)



( - ) <- if ( and ) represent the circle, the middle of the circle, the center.


I didnt know it meant center as in


(((((((((((((((((((((((((((((((( )

^ being this midpoint of the view of the solenoid from the side


LOLL!! Thank you so much for clearing this up!
if you see any flaws to what i've just posted, feel free to point it out, but everything is clear to me now! (I hope)



as for the pages and figure and example #s, I am using princeton review

You got it now!!! It's lateral movement down the center line that they are likely talking about. The BR picture is extremely helpful if you can find a friend who has the newer physics books to get a quick glance. Visuals that etch into your mind are easier to recall and work with on an exam, should a solenoid pop up in your future.

 

[Fort]

The magnetic field outside a solenoid can usually be ignored as it's very weak compared to the inside. In fact, it's theoretically zero anywhere outside any long solenoid.