Induced EMF in Changing B Field: A Paradox?

AI Thread Summary
A straight wire in a changing magnetic field can indeed have an induced emf, contingent on the alignment of the electric field with the wire. When shaped into a square loop centered in a changing B field, the induced electric field can vary based on the loop's distance from the center, suggesting differing emf values. However, according to Faraday's law, the emf induced should remain consistent regardless of the loop's position, as the area and rate of change of the magnetic field are constant. This leads to a perceived contradiction between the varying induced electric field and the uniform emf predicted by Faraday's law. The discussion highlights the complexities of electromagnetic induction and the need for careful consideration of field configurations.
pythagoras88
Messages
15
Reaction score
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
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.
 
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.\phi\widehat{}. 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, \epsilon=-d\Phi/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!
 
Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
Back
Top