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Lenz law

http://www.ocr.org.uk/Images/171758-unit-h556-03-unified-physics-sample-assessment-materials.pdf
I don't really understand question 5bii- please could someone explain (mark scheme at bottom of pdf)
Original post by runny4
http://www.ocr.org.uk/Images/171758-unit-h556-03-unified-physics-sample-assessment-materials.pdf
I don't really understand question 5bii- please could someone explain (mark scheme at bottom of pdf)


The marks scheme seems pretty clear.

the magnetic field is pointing from left to right
the change in the magnetic field is that it is becoming weaker
the induced current tries to oppose the change (according to lenz law)
therefore the induced current must be in the direction which would produce a magnetic field pointing from left to right
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runny4
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Original post by Joinedup
The marks scheme seems pretty clear.

the magnetic field is pointing from left to right
the change in the magnetic field is that it is becoming weaker
the induced current tries to oppose the change (according to lenz law)
therefore the induced current must be in the direction which would produce a magnetic field pointing from left to right


But then how do you work out that the current is anticlockwise- you can't use flemings right hand rule because you don't know the direction the coil is being rotated
Original post by runny4
But then how do you work out that the current is anticlockwise- you can't use flemings right hand rule because you don't know the direction the coil is being rotated


in section 5.B you should be looking at fig 5.3

the rotating coil was shown in fig 5.1 which was for section 5.A
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runny4
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Original post by Joinedup
in section 5.B you should be looking at fig 5.3

the rotating coil was shown in fig 5.1 which was for section 5.A


I know that fig 5.1 is not linked to this part but I still don't know how when the field is collapsing you can work out the direction of the induced current just by one piece of information- (the north and south poles of the magnet)
Original post by runny4
I know that fig 5.1 is not linked to this part but I still don't know how when the field is collapsing you can work out the direction of the induced current just by one piece of information- (the north and south poles of the magnet)


righthandgrip.png

Original post by runny4
I know that fig 5.1 is not linked to this part but I still don't know how when the field is collapsing you can work out the direction of the induced current just by one piece of information- (the north and south poles of the magnet)


You have the direction of the magnetic field..

−ΔϕΔt=EMF-\frac{\Delta \phi}{\Delta t}=EMF

Where ϕ=∫B.dA\phi=\displaystyle \int B . dA
(edited 8 years ago)
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runny4
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Original post by Joinedup
righthandgrip.png



Thank you so much for putting so much effort into explaining that to me. I really understand it now- I never even thought of using the Right hand grip rule.

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