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# Lenz's law

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1. http://www.ocr.org.uk/Images/291835-...-june-2016.pdf

On line 47 the article says 'this is not a case of generating electrical energy from nothing'. I know this is because of Lenz's law, but can any one explain this further to me?
2. (Original post by pippabethan)
http://www.ocr.org.uk/Images/291835-...-june-2016.pdf

On line 47 the article says 'this is not a case of generating electrical energy from nothing'. I know this is because of Lenz's law, but can any one explain this further to me?
You essentially have a current carrying wire (however the current is provided by the ions in the magnetosphere caused by solar radiation) in a magnetic field, this means flux lines will be cut due to the magnetosphere and this causes a change in flux. From Faraday's Law the rate of change of flux is proportional to the induced emf. This induced emf (and the current that comes along with it) will oppose the original supply p.d./current due to Lenz's law. The reason it provided enrgy from almost nothing is that the supply current and magnetic field are 'natural' in the fact they occur in space without humans providing them.

Hope this helps
3. (Original post by kennz)
Hope this helps
It does; a lot! Thank you so much
4. (Original post by pippabethan)
It does; a lot! Thank you so much
No worries, good luck for the exam
5. (Original post by kennz)
This induced emf (and the current that comes along with it) will oppose the original supply p.d. due to Lenz's law.
Another quick question: what causes the supply p.d.? Sorry, I find this topic difficult!
6. (Original post by pippabethan)
Another quick question: what causes the supply p.d.? Sorry, I find this topic difficult!
The coil is charged by collisions with ions in the ionosphere, which means there is a transfer of energy when the coil gains charge, this means there is a p.d. which then causes a supply current. I.e. the supply p.d. causes the supply current, therefore a p.d. always causes a current even the induced emf causes a current which both oppose the supply. Note that this electrodynamic tether can be used as a generator or motor.

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