I am given this question:
On the second to last line, it asked for an electric field. However, I'm wondering where does the electric field come from?
Can somebody give me an idea? I know that a varying magnetic field produces an electric field, but the way the question is worded doesn't suggest it's asking for the electric field produced by the varying magnetic field (since it seems to suggest that the magnitude of electric field varies with "distance r
The electric field $\vec E$ appears in Faraday's law
$\displaystyle \oint_{\rm loop}\vec E \cdot d\vec l= - \dfrac {d\Phi_{\rm B,surface}}{dt}$
Note that $\displaystyle \oint_{\rm loop}\vec E \cdot d\vec l$ is the induced emf.
So choose a loop which is a circle centred at the centre of the disc.
The bit about the magnetic flux due to the induced current being negligible is so that you do not need to worry about the self inductance of the disc because the induced current will oppose the change producing it - Lenz.
