Hi,(adsbygoogle = window.adsbygoogle || []).push({});

I'm currently reading griffiths and I'm a little bit confused in how it calculates emf.

EMF is initially introduced as a path integral of force/unit charge around a closed loop. This makes sense, but then he presents us with an example problem (ex 7.4)

Basically, a circuit resistor is attached to a rotating metal disc normal to a uniform magnetic field at its edge and center. (fig 7.14)

He calculates emf as the line integral of the [itex]∫f_{mag}ds[/itex] from 0 to R of the disc. However, doesn't the current flow across the entire disc? Why would we still take a line integral -- shouldn't it be a surface integral across the disc? He says this makes the flux rule difficult since it assumes current alonga well-defined path. But doesn't that apply to calculating emf as well?

When we calculated voltage with an electric field, we do a line integral but it becomes a volume integral w.r.t to the volume in question. Is there any sort of analog here?

Thanks!

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Calculating EMF and flux rule

Can you offer guidance or do you also need help?

Draft saved
Draft deleted

**Physics Forums | Science Articles, Homework Help, Discussion**