[en] Energy conversion and conservation for an electromagnetic wave traveling through a slab are analyzed. It is demonstrated that a cross term of Poynting vector may occur due to interference between forward and backward waves in the slab, and may play the leading role if the slab owns low real part of impedance. Several novel electromagnetic phenomena are predicted. For example, both reflection and transmission can be enhanced significantly even if the slab is made of lossy material. This work indicates that materials with low real part of impedance, like left-handed materials and near-zero-refractive-index materials, may hold unique electromagnetic properties and merit further exploration. Graphical abstract: .