Educator

RL Circuits

• In an RL circuit, with a battery of emf V, if the switch is closed at time t = 0, then the current in the circuit will be given by I ( t ) = ( V / R )*[ 1 – exp ( -t / T )], where T is the time constant of the RL circuit and is given by L / R. Note that the current rises gradually from 0 to a maximum value of V / R.
• After the current has reached its maximum value, if we then disconnect the battery at time t = 0, so that we end up with an RL circuit without a battery, then the current decreases in time according to I ( t ) = ( V / R )*exp( - t / T ).
• Just like a capacitor, when charged, stores electric energy in the space between the plates, an inductor, when it carries a current, stores magnetic energy. The magnetic energy stored in the inductor is ( 1 / 2 ) L I^2.