This question caused a debate in the class: EMF from a changing magnetic field

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In summary, the question regarding the electromagnetic force (EMF) generated by a changing magnetic field sparked a lively debate among students in the class, highlighting differing perspectives and interpretations of the concept.
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Physical_Fire
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Hello,
So recently our class have learnt about E.M.F induction entirely with it's equation and a classmate found a question from the internet. I honestly believe the answer is A as the magnetic field is changing rapidly, but some of my classmates believe it's B. While others believe it's C. This has caused a debate to ensue and I shared my reasoning. What does the community think is the correct answer?
1717688734147.png
 
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  • #2
What is the Relevant Equation relating EMF to the magnetic flux through the coil? Can you sketch a plot of the magnetic flux versus time while the magnet is spinning (and label the points P, Q, R on that plot)?

And based on the Relevant Equation, what do you need to do to that plot to show the EMF induced in the coil versus time? :smile:
 
  • #3
-d phi(b) / change in t. phi(b) is the change in magnetic flux. and the graph would be as attached. However, I am not sure how to label as I don't understand which has the highest emf
1717689686205.png
 
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  • #4
Good. The first vertical dotted line on the left is in the wrong place, though, and should be at the Origin (move it to the left).

Where do you think point Q could be on the graph?

EDIT -- the 3 middle points on the 2 graphs look okay, but the outer points are a bit misaligned (the bottom sine wave is asymmetrical)
 
  • #5
Q should be the second vertical line as it has the magnetic flux is changing rapidly so emf is at its max. So does that mean it's A, and I was secretly right the entire time?
 
  • #6
Physical_Fire said:
Q should be the second vertical line as it has the magnetic flux is changing rapidly so emf is at its max. So does that mean it's A, and I was secretly right the entire time?
It could be either of the zero crossings of the flux sine wave, so yes, I believe the correct answer is A.
 
  • #7
Thanks for resolving.
 
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FAQ: This question caused a debate in the class: EMF from a changing magnetic field

What is EMF and how is it generated by a changing magnetic field?

Electromotive force (EMF) is a measure of the energy provided per charge by an energy source, such as a battery or a changing magnetic field. According to Faraday's law of electromagnetic induction, a changing magnetic field within a closed loop induces an EMF in the loop. This occurs because the changing magnetic field creates an electric field that drives current through the conductor.

What is Faraday's law of electromagnetic induction?

Faraday's law states that the induced EMF in a closed circuit is directly proportional to the rate of change of the magnetic flux through the circuit. Mathematically, it can be expressed as EMF = -dΦ/dt, where Φ is the magnetic flux. The negative sign indicates the direction of the induced EMF opposes the change in magnetic flux, as described by Lenz's law.

How does the strength of the magnetic field affect the induced EMF?

The strength of the magnetic field directly affects the induced EMF. A stronger magnetic field or a faster rate of change in the magnetic field results in a greater change in magnetic flux, which in turn produces a higher induced EMF. Conversely, a weaker magnetic field or a slower rate of change will result in a lower induced EMF.

What are some practical applications of EMF generated by changing magnetic fields?

EMF generated by changing magnetic fields is utilized in various applications, including electric generators, transformers, and inductors. In electric generators, mechanical energy is converted into electrical energy through the rotation of coils in a magnetic field. Transformers use changing magnetic fields to transfer electrical energy between circuits at different voltage levels.

Are there any safety concerns related to EMF exposure from changing magnetic fields?

While EMF is a common phenomenon in electrical devices and power lines, concerns about health effects from exposure to EMF, particularly at high frequencies, have been raised. Current research has not conclusively established harmful effects from low-frequency EMF exposure, such as that from power lines. However, guidelines and safety standards are in place to limit exposure to EMF, especially in occupational settings.

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