Who or What is Doing Work on the Rod in a Superconducting MRI Magnet?

  • Thread starter vabamyyr
  • Start date
  • Tags
    Work
Please refrain from doing so in the future.In summary, when a steel rod is inserted into a magnetic field, the stored energy in the magnetic field decreases. This is due to the fact that air can store more magnetic energy than steel for a specific magnetic field. When the rod is pulled back out, the rod does work and the energy of the field increases back to its original value. The idea that a field does work and has energy is supported by scientific principles. Repeatedly letting the magnet pull and pulling the rod back out will not reduce the field strength to 0.
  • #1
vabamyyr
66
0
Suppose I have a superconducting solenoid MRI magnet (cooled with liquid helium) producing a static magnetic field around it. I approach the magnet bore with a steel rod in my hand. The rod starts to pull towards the magnet and i have to work against the pull in order not to let it attach onto the machine. Now my question is, have I reduced the energy of the static magnetic field when I've pulled the rod away from the magnet or is there some sort of compensatory mechanism that keeps the static field fixed to its nominal value? I know that the pull is largely due to the spatial gradient of the magnetic field but what or who is doing the work on the rod?
 
Physics news on Phys.org
  • #2
Hi vabamyyr! :smile:

It's the same as carrying a rod downstairs …

the potential energy of the rod (gravitational or magnetic) changes, but since PE is just another name for work done by a conservative field, that's another way of saying that work is done by the field.

Work is also done by you, and so long as the two cancel, the KE remains zero, and the rod stays in your hand. :wink:
 
  • #3
When a steel rod is inserted into a magnetic field, the stored energy in the magnetic field decreases. The stored energy is the integral

Stored magnetic energy = 1/2 ∫B·H dV where integral is over all space.

Air can store more magnetic energy than steel for a specific B. So inserting a steel rod reduces strored energy.

Bob S
 
  • #4
I am very, very uncomfortable with the idea that a field does work. Next thing, we'll have to say that a field has energy.

I think the situation is exactly that of a susceptible object in any other field, say the gravitational field about the Earth. Drop something, pick it up... where did the energy come from? Was it in the gravitational field or was it a property of the object which was raised on high?

In your magnetic field, a magnet and a steel bar find themselves attracted to one another; if you had collected all the energy converted in the approach you could use it again to get yourself out.
 
Last edited:
  • #5
does that mean when I repeatedly let the magnet pull the rod and me pulling it back ultimately reduce the field strength to 0?
 
  • #6
vabamyyr said:
does that mean when I repeatedly let the magnet pull the rod and me pulling it back ultimately reduce the field strength to 0?
No. Every time you insert the rod work is done on the rod and the energy of the field decreases. Every time you pull the rod back out the rod does work and the energy of the field increases back to where it was.
 
Last edited:
  • #7
arithmetix said:
I am very, very uncomfortable with the idea that a field does work. Next thing, we'll have to say that a field has energy.
The field does have energy. See: http://farside.ph.utexas.edu/teaching/em/lectures/node89.html"
 
Last edited by a moderator:
  • #8
thank you DaleSpam
 

1. What is the purpose of "What, who is doing the work?"

The purpose of asking "What, who is doing the work?" is to gain a better understanding of the specific tasks being performed and the individuals or entities responsible for carrying them out. This information is important in order to track progress, assign credit, and identify areas for improvement.

2. How do scientists determine "who" is doing the work?

Scientists typically determine "who" is doing the work by keeping detailed records and documentation of each person's contributions. This can include lab notebooks, data collection sheets, and written reports. In some cases, scientists may also use specialized software or databases to track and assign credit for work.

3. What role does collaboration play in "what, who is doing the work?"

Collaboration plays a crucial role in determining "what, who is doing the work?" as many scientific projects require multiple individuals with different expertise to work together. In these cases, it is important to clearly define each person's role and responsibilities to ensure efficient teamwork and accurate credit assignment.

4. How do scientists address conflicts or discrepancies in "what, who is doing the work?"

If conflicts or discrepancies arise in determining "what, who is doing the work?", scientists may refer to their documentation and records to resolve the issue. In cases where there is a disagreement, the individuals involved may need to have a discussion to clarify their roles and contributions.

5. Why is it important for scientists to track "what, who is doing the work?"

Tracking "what, who is doing the work?" is important for several reasons. Firstly, it allows for accurate credit assignment, which is crucial for scientific integrity. Additionally, it helps to monitor progress and identify any issues or areas for improvement. It also allows for transparency and accountability within the scientific community.

Similar threads

How to explain the Quantum Mechanics/Math of the stages of MRI imaging
    • Advanced Physics Homework Help
Replies
4
Views
1K
Placing an AC magnetic field inside a static DC field
    • Electromagnetism
Replies
8
Views
983
B Permanent magnets and energy question
    • Classical Physics
Replies
16
Views
1K
The role of permanent magnets coupled with solenoids
    • Electrical Engineering
Replies
7
Views
2K
I How Does an MRI Work and Differentiate Between Different Tissues?
    • Other Physics Topics
Replies
14
Views
2K
What is the equation for torque in an MRI scanner?
    • Mechanics
Replies
1
Views
3K
Why does the Japanese Maglev train use superconducting magnets
    • Electrical Engineering
Replies
1
Views
1K
MRI Electromagnet Interference in a Figure-8 cable
    • Electromagnetism
Replies
2
Views
2K
Measuring Magnetic Moment of a Torque Rod
    • Mechanics
Replies
2
Views
7K
Working electrical engineer transitioning to physics?
    • STEM Academic Advising
Replies
5
Views
1K

Hot Threads

Recent Insights

Back
Top