An electrical circuit consisting of a coil with inductance $$L$$ and an resistor $$R$$ connected in series to the coil. In addition, a voltage source which supplies the voltage $$U_0$$ as soon as the circuit is closed with a switch. Then a time dependent current $$I(t)$$ flows through the coil and the resistor. The current does not have its maximum value immediately, but increases slowly due to Lenz's law.