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# Flux and Current: OCR Physics B watch

1. On the syllabus for OCR Physics B it states that candidates need to be able to illustrate the relationship between flux, induced emf and current.

The relationship between flux and emf is well-known and obvious: E = - dflux/dt and I am able to plot it on a graph without any problem (except am I the only person who turns emf upside down because it’s equal to the NEGATIVE rate of change of flux? i.e. Where flux = sin then emf = - cos. Lots of textbooks just show a sin/cos relationship which is the opposite of the formula?)

Anyway, my real question is what is the relationship between current and flux? I would have thought that since V=IR then current would also be proportional to the rate of change of flux. The problem is that no textbook defines this and my teacher doesn’t seem to know either.

Any help would be greatly appreciated,

Thanks, tom
2. (Original post by tomhitchings)
On the syllabus for OCR Physics B it states that candidates need to be able to illustrate the relationship between flux, induced emf and current.

The relationship between flux and emf is well-known and obvious: E = - dflux/dt and I am able to plot it on a graph without any problem (except am I the only person who turns emf upside down because it’s equal to the NEGATIVE rate of change of flux? i.e. Where flux = sin then emf = - cos. Lots of textbooks just show a sin/cos relationship which is the opposite of the formula?)

Anyway, my real question is what is the relationship between current and flux? I would have thought that since V=IR then current would also be proportional to the rate of change of flux. The problem is that no textbook defines this and my teacher doesn’t seem to know either.

Any help would be greatly appreciated,

Thanks, tom
Cant you write in normal font ?

The answer is : current is proportional to the rate of change of flux. (thats what i have in my exercise book...my techer went to cambs so i hope she would know!)

Thats all you need to say.
3. (Original post by chud)
Cant you write in normal font ?

The answer is : current is proportional to the rate of change of flux. (thats what i have in my exercise book...my techer went to cambs so i hope she would know!)

Thats all you need to say.
We went over this today and reached a different conclusion. Since magnetic field is determined by current, then flux and current are proportional, and so emf is proportional to the rate of change of both current and flux...

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