An RL circuit consists of an ideal switch, a resistor of resistance \(R\), an inductor of inductance \(L\), and an ideal battery of constant emf \(\varepsilon\), all connected in series. At time \(t = 0\), the switch is closed. In terms of the circuit's time constant \(\tau = \dfrac{L}{R}\), at what time \(t\) does the energy stored in the magnetic field of the inductor reach half of its maximum steady-state value?