Please help, why does polarity of a magnet switch when going through a coil?

Watch
Minnie16
Badges: 8
Rep:
?
#1
Report Thread starter 3 years ago
#1
Hi, could you please write exactly what happens and why when a magnet slowly falls through an electric coil.....thanks!
0
reply
Kyx
Badges: 6
Rep:
?
#2
Report 3 years ago
#2
(Original post by Jas1947)
Hi, could you please write exactly what happens and why when a magnet slowly falls through an electric coil.....thanks!
The magnet induces a current in the coil, which itself produces a magnetic field. This magnetic field opposes the field of the magnet so the magnet is repelled. This is why if it is falling, it slows down


Posted from TSR Mobile
0
reply
Minnie16
Badges: 8
Rep:
?
#3
Report Thread starter 3 years ago
#3
(Original post by Kyx)
The magnet induces a current in the coil, which itself produces a magnetic field. This magnetic field opposes the field of the magnet so the magnet is repelled. This is why if it is falling, it slows down


Posted from TSR Mobile
Thank you but why does emf become negative as the magnetic is leaving the coil according to a emf vs time graph?

Posted from TSR Mobile
0
reply
Kyx
Badges: 6
Rep:
?
#4
Report 3 years ago
#4
(Original post by Jas1947)
Thank you but why does emf become negative as the magnetic is leaving the coil according to a emf vs time graph?

Posted from TSR Mobile
If the current and voltage is in one direction as it enters, it will go in the other direction as it leaves.

If the magnet is out, the coil doesn't want it in, so current travels in the direction that causes the magnet to be repelled. But once the magnet is in, the coil doesn't want it to leave, so the current flips around to attract the magnet back in

The current in a solenoid is always such that the resulting magnetic field opposes that which caused the current.

If a magnet goes in North side first, then the coil will have North at the point where it is entering (the top) to repel it. When the magnet is leaving, the coil will have North at the bottom to attract it.

(Hope that makes sense )


Posted from TSR Mobile
0
reply
Minnie16
Badges: 8
Rep:
?
#5
Report Thread starter 3 years ago
#5
(Original post by Kyx)
If the current and voltage is in one direction as it enters, it will go in the other direction as it leaves.

If the magnet is out, the coil doesn't want it in, so current travels in the direction that causes the magnet to be repelled. But once the magnet is in, the coil doesn't want it to leave, so the current flips around to attract the magnet back in

The current in a solenoid is always such that the resulting magnetic field opposes that which caused the current.

If a magnet goes in North side first, then the coil will have North at the point where it is entering (the top) to repel it. When the magnet is leaving, the coil will have North at the bottom to attract it.

(Hope that makes sense )


Posted from TSR Mobile
Ah yes this answer is what I've been looking for! Thank you! But in an exam would I be allowed to say the coil doesn't want the magnet to leave? Or should I say that the polarity of the coil switched and this is because.....


Posted from TSR Mobile
0
reply
Kyx
Badges: 6
Rep:
?
#6
Report 3 years ago
#6
(Original post by Jas1947)
Ah yes this answer is what I've been looking for! Thank you! But in an exam would I be allowed to say the coil doesn't want the magnet to leave? Or should I say that the polarity of the coil switched and this is because.....


Posted from TSR Mobile
I think you just need to state the law:

The current in a solenoid is always such that it produces a magnetic field that opposes the magnetic field that induced the current.

Also, if you think about it, if the current didn't oppose the magnetic field that caused it, it would be in the other direction, which would generate a larger current. This would then generate a larger current (and the magnet would accelerate faster and faster). This means you would be getting energy into the wire without the magnet losing any. Free energy! Not allowed :no:


Posted from TSR Mobile
0
reply
Kyx
Badges: 6
Rep:
?
#7
Report 3 years ago
#7
I'm not sure what the law is called, might be Faraday's law. I'll find out tomorrow


Posted from TSR Mobile
0
reply
Kyx
Badges: 6
Rep:
?
#8
Report 3 years ago
#8
(Original post by Jas1947)
Hi, could you please write exactly what happens and why when a magnet slowly falls through an electric coil.....thanks!
It's Lenz's Law:

Name:  ImageUploadedByStudent Room1494834692.316770.jpg
Views: 79
Size:  167.9 KB


Posted from TSR Mobile
1
reply
Minnie16
Badges: 8
Rep:
?
#9
Report Thread starter 3 years ago
#9
(Original post by Kyx)
It's Lenz's Law:

Name:  ImageUploadedByStudent Room1494834692.316770.jpg
Views: 79
Size:  167.9 KB


Posted from TSR Mobile
Yes thank you!! could you please show where figure 2 is aswell please... Thanks

Posted from TSR Mobile
0
reply
Kyx
Badges: 6
Rep:
?
#10
Report 3 years ago
#10
(Original post by Jas1947)
Yes thank you!! could you please show where figure 2 is aswell please... Thanks

Posted from TSR Mobile
I will do once I'm back home
0
reply
Kyx
Badges: 6
Rep:
?
#11
Report 3 years ago
#11
(Original post by Jas1947)
Yes thank you!! could you please show where figure 2 is aswell please... Thanks

Posted from TSR Mobile
Name:  ImageUploadedByStudent Room1494869294.457969.jpg
Views: 74
Size:  197.7 KB


Posted from TSR Mobile
0
reply
Minnie16
Badges: 8
Rep:
?
#12
Report Thread starter 3 years ago
#12
Thank you!!

Posted from TSR Mobile
0
reply
Kyx
Badges: 6
Rep:
?
#13
Report 3 years ago
#13
(Original post by Jas1947)
Thank you!!

Posted from TSR Mobile
No problem


Posted from TSR Mobile
0
reply
Eimmanuel
Badges: 13
Rep:
?
#14
Report 3 years ago
#14
(Original post by Kyx)
If the current and voltage is in one direction as it enters, it will go in the other direction as it leaves.

If the magnet is out, the coil doesn't want it in, so current travels in the direction that causes the magnet to be repelled. But once the magnet is in, the coil doesn't want it to leave, so the current flips around to attract the magnet back in

The current in a solenoid is always such that the resulting magnetic field opposes that which caused the current.

If a magnet goes in North side first, then the coil will have North at the point where it is entering (the top) to repel it. When the magnet is leaving, the coil will have North at the bottom to attract it.

(Hope that makes sense )


Posted from TSR Mobile
(Original post by Kyx)
It's Lenz's Law:

Name:  ImageUploadedByStudent Room1494834692.316770.jpg
Views: 79
Size:  167.9 KB


Posted from TSR Mobile
I believe a lot of students have learnt that "Lenz's law is the result of conservation of energy" but I would like to propose a different view.

Name:  Re_ [Phys-L] Lenz's law and conservation of energyjpg_Page1.jpg
Views: 168
Size:  375.2 KB
This is a discussion among physics teachers in a physics forum and I find that it is an interesting discussion and has some interesting answers, so I share it here.

If your exam board is stating that you need to explain Lenz's law through conservation of energy, don't propose another view.

A lot of physics textbooks explain Lenz's law saying that law of conservation of energy would be violated if Lenz's law is not applied. I find that the analysis is usually incomplete because the magnetic field is NOT taken into account. I personally believe if a complete analysis that include the electromagnetic field, energy would be conserved. Just my two cents of opinions.
1
reply
Minnie16
Badges: 8
Rep:
?
#15
Report Thread starter 3 years ago
#15
(Original post by Eimmanuel)
I believe a lot of students have learnt that "Lenz's law is the result of conservation of energy" but I would like to propose a different view.

Name:  Re_ [Phys-L] Lenz's law and conservation of energyjpg_Page1.jpg
Views: 168
Size:  375.2 KB
This is a discussion among physics teachers in a physics forum and I find that it is an interesting discussion and has some interesting answers, so I share it here.

If your exam board is stating that you need to explain Lenz's law through conservation of energy, don't propose another view.

A lot of physics textbooks explain Lenz's law saying that law of conservation of energy would be violated if Lenz's law is not applied. I find that the analysis is usually incomplete because the magnetic field is NOT taken into account. I personally believe if a complete analysis that include the electromagnetic field, energy would be conserved. Just my two cents of opinions.
Thank you

Posted from TSR Mobile
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Do you have the space and resources you need to succeed in home learning?

Yes I have everything I need (398)
56.29%
I don't have everything I need (309)
43.71%

Watched Threads

View All