In the circuit shown, an ideal battery of EMF \(\mathcal{E}\) is connected in series with an open switch \(S\) and a resistor of resistance \(R_1 = R\). In parallel with this combination are two branches: a middle branch containing a resistor of resistance \(R_2 = 2R\), and a right branch containing an ideal inductor of inductance \(L\) connected in series with a resistor of resistance \(R_3 = R\). The switch \(S\) is closed and the circuit is allowed to reach steady state. At time \(t = 0\), the switch \(S\) is suddenly opened. Immediately after the switch is opened, what is the magnitude of the induced EMF across the inductor?