Electromagnetism issues need clearing up

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SUMMARY

This discussion focuses on the relationship between mutual inductance, the number of turns in coils, the current in a primary coil, and the induced electromotive force (emf) in a secondary coil, particularly in the context of transformers. The key equations presented include the magnetic field strength formula, B = (μ₀NI)/(2πr), and the emf equations E = -dψ/dt = -L(dI/dt) for self-inductance and E = M(dI/dt) for mutual inductance. The user expresses confusion regarding the definitions and relationships of inductance, specifically how mutual inductance (M) relates to self-inductance (L).

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  • Understanding of electromagnetic theory and principles
  • Familiarity with the concepts of inductance and mutual inductance
  • Knowledge of the equations governing magnetic fields and emf
  • Basic grasp of transformer operation and coil configurations
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  • Study the derivation and applications of mutual inductance in transformers
  • Explore the relationship between self-inductance and mutual inductance in coupled coils
  • Learn about the role of permeability of free space (μ₀) in electromagnetic calculations
  • Investigate practical examples of inductance in electrical circuits and devices
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Students of physics, electrical engineers, and anyone involved in the design or analysis of electromagnetic systems, particularly those working with transformers and inductive components.

ppyadof
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In electromagnetism, when there is an emf is induced in a secondary coil from a current flowing in a nearby primary coil (such as in a transformer), then how is the mutual inductance, number of turns of each coil, the current in the primary coil, and the emf in the secondary coil related?

From the reading that I have been doing, I think that for a single coil:
[tex]B = \frac{u_0NI}{2 \pi r}[/tex]
Where the [itex]u_0[/itex] is the permeability of free space (I don't know how to get the proper symbol), [itex]N[/itex] is the number of turns, and [itex]B[/itex] is the magnetic field strength.

From what I have gathered from the reading, is:
[tex]E = -\frac{d \psi}{dt} = -L \frac{dI}{dt}[/tex]
Where I have used [itex]E[/itex] for emf, and psi for the flux (I don't know how to get the convention symbol), and [itex]L[/itex] is the inductance of the secondary coil, however, I am unsure as to how the mutual inductance (M) is related to the inductance (L).

I think the problem is that when people speak of inductance, I am unsure what they mean the inductance of.

The reason why I am asking is that I have a question which uses this idea, but I am so close to getting it, that I would rather not post the problem in the homework section.

Thanks in advance.
 
Last edited:
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ppyadof said:
In electromagnetism, when there is an emf is induced in a secondary coil from a current flowing in a nearby primary coil (such as in a transformer), then how is the mutual inductance, number of turns of each coil, the current in the primary coil, and the emf in the secondary coil related?

From the reading that I have been doing, I think that for a single coil:
[tex]B = \frac{u_0NI}{2 \pi r}[/tex]
Where the [itex]u_0[/itex] is the permeability of free space (I don't know how to get the proper symbol), [itex]N[/itex] is the number of turns, and [itex]B[/itex] is the magnetic field strength.

From what I have gathered from the reading, is:
[tex]E = -\frac{d \psi}{dt} = -L \frac{dI}{dt}[/tex]
Where I have used [itex]E[/itex] for emf, and psi for the flux (I don't know how to get the convention symbol), and [itex]L[/itex] is the inductance of the secondary coil, however, I am unsure as to how the mutual inductance (M) is related to the inductance (L).

I think the problem is that when people speak of inductance, I am unsure what they mean the inductance of.

The reason why I am asking is that I have a question which uses this idea, but I am so close to getting it, that I would rather not post the problem in the homework section.
L, self inductance, is the ratio of induced emf in an inductor (coil) to rate of change of current in that inductor: Emf = L dI/dt

Mutual inductance relates to two coils in which a change of current in one coil induces an emf in the other. Emf = MdI/dt where Emf is the emf in the other coil.

AM
 
[itex]\phi[/itex]?
 

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