Electromagnetic Induction Problem (Very Introductory)

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Homework Statement


Look at the following diagram:
Untitled-3.jpg


- copy the diagram and then label the poles for the induced magnetic field and the direction of the induced current
- explain what would happen to the magnetic field and the current if the direction of motion of the magnet reversed
- explain what would happen to the magnetic field and the current if the magnet is moved more quickly in the same direction
- explain what would happen to the magnetic field and the current if the magnet is moved rapidly back and forth


5. Relevant equations

Lenz's Law

The Attempt at a Solution


IMG_0493.JPG


- Reversing the direction of motion of the magnet reverses the direction of the current. The induced current will produce an induced magnetic field that will either attract the permanent magnet or repel it.

- According to Lenz’s law, when a current is induced in a coil by a changing magnetic field, the induced current must produce a magnetic field that opposes the change that produced it. In other words, there must be an induced magnetic field produced by the induced current that will resist the motion of the bar magnet, not accelerate it.

- If the magnet is moved back and forth into and then out of the coil, an alternating current can be produced.


This is what I've come up with according to my own reasoning of the lesson.
Can someone look over my work and help me in whichever areas I may not be understanding properly?
 

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Answers and Replies

  • #2
Merlin3189
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- copy the diagram and then label the poles for the induced magnetic field and the direction of the induced current
- explain what would happen to the magnetic field and the current if the direction of motion of the magnet reversed
- explain what would happen to the magnetic field and the current if the magnet is moved more quickly in the same direction
- explain what would happen to the magnetic field and the current if the magnet is moved rapidly back and forth

5. Relevant equations Lenz's Law

The Attempt at a Solution


View attachment 221439 √ 1

- Reversing the direction of motion of the magnet reverses the direction of the current. The induced current will produce an induced magnetic field that will either attract the permanent magnet or repel it. √ 2

- According to Lenz’s law, when a current is induced in a coil by a changing magnetic field, the induced current must produce a magnetic field that opposes the change that produced it. In other words, there must be an induced magnetic field produced by the induced current that will resist the motion of the bar magnet, not accelerate it. √ 1 & 2
- If the magnet is moved back and forth into and then out of the coil, an alternating current can be produced. √ 4

This is what I've come up with according to my own reasoning of the lesson.
Looks like you have a very good understanding.
Only question 3 remains unanswered. How does the speed of movement of the magnet affect things?

Edit: (This is Michael Faraday's observation.)
 
  • #3
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The magnet field of a bar magnet is strongest near the poles. As the poles approach the coil, the field will increase in strength. If the magnetic field increases rapidly, then the induced current will be stronger. I think this would answer the third question. Thank you for your help!
 
  • #4
Merlin3189
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Yes, the induced emf is proportional to the rate of change of magnetic flux.
So if the magnet moves faster, greater rate of change of flux, greater emf and induced current, and greater repulsive force.
 

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