Lenz law and reduction of orbit height?? Watch

sarah99630
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pleaaaseeee help me with part b...by elaborating how exactly the key points in the answer come about. Much appreciation for the help. im so confused!I only understand that there's going to be a force experienced due to the current cutting the magnetic field, thats all I can tell. Name:  image-dacceaec-b2d5-449b-8c95-8ce735ed92431255375761-compressed.jpg.jpeg
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DrSebWilkes
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Let's use a less complicated example. If you have a wire (which can conduct etc. etc.) and move it inside / through a magnetic field, I'm sure you've seen the demonstration that there is a current that is produced. Brilliant, we can generate power, whipee! But ... you know ... what if I just kept going? I mean I could have unlimited power, right? Because there isn't any resistance ... so if I had a loop I could push the wire around and around and around and create a perpetual motion machine that makes me loads of electricity in complete violation of the 1st law of thermodynamics.

Yeah ... no. So Lenz law comes about because as the current (which will be opposite in direction to motion) will generate it's own magnetic field. This magnetic field clashes with the one it's already in, and you know that causes a force. This force is equal, and opposite, to the force you are applying to the wire to accelerate it. Now, if it was already moving that means you have kinetic energy; which we can understand? And then if suddenly generate a voltage (and all that jazz) then that's another form of energy so it has to come from your kinetic. That's the otherside of the coin. The force exerted onto the wire slows it down and converts that loss of energy intol usable (or otherwise) voltage.

So as the wire conducts, and uses that voltage, the kinetic energy of the shuttle must go down ... which means it's orbit goes down.
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sarah99630
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(Original post by DrSebWilkes)
Let's use a less complicated example. If you have a wire (which can conduct etc. etc.) and move it inside / through a magnetic field, I'm sure you've seen the demonstration that there is a current that is produced. Brilliant, we can generate power, whipee! But ... you know ... what if I just kept going? I mean I could have unlimited power, right? Because there isn't any resistance ... so if I had a loop I could push the wire around and around and around and create a perpetual motion machine that makes me loads of electricity in complete violation of the 1st law of thermodynamics.

Yeah ... no. So Lenz law comes about because as the current (which will be opposite in direction to motion) will generate it's own magnetic field. This magnetic field clashes with the one it's already in, and you know that causes a force. This force is equal, and opposite, to the force you are applying to the wire to accelerate it. Now, if it was already moving that means you have kinetic energy; which we can understand? And then if suddenly generate a voltage (and all that jazz) then that's another form of energy so it has to come from your kinetic. That's the otherside of the coin. The force exerted onto the wire slows it down and converts that loss of energy intol usable (or otherwise) voltage.

So as the wire conducts, and uses that voltage, the kinetic energy of the shuttle must go down ... which means it's orbit goes down.
OMG I read so many articles on this and didn't get it! You're amazing at explaining (another Walter lewin). Thank you so much!!!! )) Yaaay I never thought I'd understand that!
Quick question please, to get the direction of the current produced, we use the Fleming's LHR right? (we will be using the direction of the field of the bar magnet? and by that direction are we using the direction in which the north pole is moving or direction of the field lines? N-S.) then once we get the direction of the current, can I use the right hand thumb rule to get the direction of the magnetic field?
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DrSebWilkes
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(Original post by sarah99630)
OMG I read so many articles on this and didn't get it! You're amazing at explaining (another Walter lewin). Thank you so much!!!! )) Yaaay I never thought I'd understand that!
Quick question please, to get the direction of the current produced, we use the Fleming's LHR right? (we will be using the direction of the field of the bar magnet? and by that direction are we using the direction in which the north pole is moving or direction of the field lines? N-S.) then once we get the direction of the current, can I use the right hand thumb rule to get the direction of the magnetic field?
Haha thanks!

There is a flemings right hand rule which is kinda similar - the force is kinda like a rocket engine so the movement / motion will be opposite in direction to the force. Try it with your hands remembering to keep the direction of the current the same. Maybe that helps a bit?

The thumb rule can help you understand why it happens though, but I'm sure it over-complicates it a bit.
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sarah99630
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(Original post by DrSebWilkes)
Haha thanks!

There is a flemings right hand rule which is kinda similar - the force is kinda like a rocket engine so the movement / motion will be opposite in direction to the force. Try it with your hands remembering to keep the direction of the current the same. Maybe that helps a bit?

The thumb rule can help you understand why it happens though, but I'm sure it over-complicates it a bit.
Got it!! MUCH APPRECIATION.
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