Induced EMF in Changing B Field: A Paradox?

In summary, the question is whether a straight wire in a changing perpendicular magnetic field can have an induced emf. The answer is that it could, as a changing magnetic field also implies a changing electric field. However, if the wire is shaped into a square loop at the center of the field, the induced E field can be found to be dependent on the distance from the center. This seems to contradict Faraday's law which states that the induced emf is the same regardless of the placement of the loop in the field.
  • #1
pythagoras88
17
0
Does a straight wire in changing B field(the field is perpendicular to the wire) has an induced emf?
 
Physics news on Phys.org
  • #2
It could. A changing magnetic field implies that there exists a changing electric field. If the electric field is aligned with a parallel component (which may or may not happen since we only know that the wire is normal to the B field) then it will induce a current in the wire.
 
  • #3
Now let's say the wire is shaped into a square loop with the center coinciding with the center of the changing B field(again, B field perpendicular to square).Taking circular amperian loop with radius s from the center of the magnetic field, the Induced E field can be found to be
E=-s/2. dB/dt.[tex]\phi\widehat{}[/tex]. Assuming the B field is uniform throughout the plane, and is changing at constant rate. So, if the square loop is put at a distance from the center of the field, then the induced E field in it seems to be different as E has the dependence on s. Thus, result in a seemingly difference emf induced if the loop is placed at different region.

However, from faraday's law, [tex]\epsilon[/tex]=-d[tex]\Phi[/tex]/dt. Since the area enclosed by the loop is the same plus the rate of change of B field is the same, it implies that the emf induced is the same in the loop no matter where it is placed in the B field.

hmm... why there seems to be a contradiction?

Sorry for the long winded qn!
 

Related to Induced EMF in Changing B Field: A Paradox?

1. What is the "wire in changing B field" phenomenon?

The "wire in changing B field" phenomenon refers to the behavior of an electrically charged wire when it is placed in a magnetic field that is changing over time. This can result in the wire experiencing a force and possibly even inducing an electric current in the wire.

2. How does a changing magnetic field affect a wire?

When a wire is placed in a changing magnetic field, it will experience a force due to the interaction between the magnetic field and the electric charges in the wire. This force is known as the Lorentz force and can cause the wire to move or even induce an electric current in the wire.

3. Why does a wire experience a force in a changing magnetic field?

A wire experiences a force in a changing magnetic field because of the interaction between the magnetic field and the electric charges in the wire. Moving electric charges create a magnetic field, and when this magnetic field interacts with the external magnetic field, it results in a force on the wire.

4. How does the direction of the wire affect its behavior in a changing magnetic field?

The direction of the wire does not affect its behavior in a changing magnetic field. The force on the wire will always be perpendicular to both the direction of the magnetic field and the current in the wire, regardless of the orientation of the wire.

5. What practical applications does the "wire in changing B field" phenomenon have?

The "wire in changing B field" phenomenon has many practical applications, including electric generators and motors that use the interaction between a wire and a changing magnetic field to produce electricity or mechanical motion. It is also used in devices such as transformers and in medical imaging techniques like MRI. Understanding this phenomenon is crucial for many technological advancements in fields such as energy, transportation, and healthcare.

Similar threads

Replies
8
Views
474
  • Introductory Physics Homework Help
Replies
14
Views
1K
  • Introductory Physics Homework Help
Replies
2
Views
1K
  • Introductory Physics Homework Help
Replies
3
Views
1K
  • Introductory Physics Homework Help
Replies
16
Views
417
  • Introductory Physics Homework Help
Replies
11
Views
1K
  • Introductory Physics Homework Help
Replies
2
Views
800
  • Introductory Physics Homework Help
Replies
16
Views
248
  • Introductory Physics Homework Help
Replies
11
Views
814
  • Introductory Physics Homework Help
Replies
2
Views
819
Back
Top