Kirchoff analysis in faraday law for RL circuit

batterieselectric-circuitselectrical-resistanceinductancevoltage

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Faraday law state that $$\epsilon_L=\oint \vec{E} \cdot d\vec{l}=-\frac{d\phi}{dt}=-L\frac{dI}{dt}.$$

So by kirchoff's analysis, isn't the equation would be like
$$\oint \vec{E}\cdot d\vec{l}=0-IR+\epsilon_c=-L\frac{dI}{dt}$$
as potential drop in resistor and potential gain in cell

But why it is instead $$0+IR-
\epsilon_c=-L\frac{dI}{dt}$$

Where

$\epsilon_L=$emf by inductor

$\epsilon_c=$emf of cell

$\oint=$ closed integral of the circuit in clockwise direction

Asumption: inductor are made of super conducting wire (0 ohm resistance)

Best Answer

This is a still from Walter Lewin's video 8.02x - Lect 20 - Inductance, RL Circuits, Magnetic Field Energy.

He evaluates $\displaystyle \int \vec{E} \cdot d\vec{l}$ for each of the three circuit elements starting at the dot to the left of the current arrow at the top of the circuit digram, moving in a clockwise direction which is the same as the current direction label.

For the inductor since $\vec E=0$ the integral is zero.
For the resistor the direction of the path taken $d\vec \ell$ is the same as the direction of the electric field so the integral is positive $+IR$.
For the cell the direction of the electric field is opposite to that of the path taken and so the integral is negative, $-\epsilon _{\rm c}$.

This leads to the resulting equation, $\,0+IR-\epsilon_c=-L\frac{dI}{dt}$

Note that in this derivation Walter Lewin is evaluating $\displaystyle \int \vec{E} \cdot d\vec{l}$ which you will remember is equal to $\color {red}{minus}$ the change in potential, which as a differential equation is the electric field is equal to $\color {red}{minus}$ the potential gradient.