In physical terms, EMFs can be regarded as circuit elements which put energy into a circuit and a resistor R as an element which removes energy from a circuit. The energy is dissipated in the resistor as heat. In AC circuits we have the additional circuit elements, capacitance C and inductance L, which store energy in electric and magnetic fields respectively. C and L are referred to as reactive elements while R is a resistive element. All three of these element are considered passive elements. We will encounter active circuit elements in the lectures to follow. For simplicity we will ignore radiation that might be emitted by high frequency circuits.