In our definition of the ground loop we said that a ground loop is created whenever a closed electrical path, consisting of ground wire (or shields) of a system and the ground plane, exist. In fig 16.5(a) we indicated that such a path can consist of an ohmic conducting path and the ground plane. However, owing to capacitive coupling, a closed electrical can also exist even if there is n apparently complete ohmic conducting path( i.e., even though the measurement system is ohmically connected to ground only at a single point). For example, let us examine an amplifier, as shown in Fig. 16.7, with an input signal ground connected to earth ground at point 1 and a shield surrounding the amplifier that is not connected to earth ground. Note that there is still a complete current path (loop) from the ground lead within ampllifier 1 to a second ground point, 4 through the mutual capacitances connecting the ground lead and shield(c12) and the shield and the ground plane(c23) thus a ground loop through path 1-2-3-4-1 does indeed exist. If an ac potential difference exist between the ground point 1 and 4 , a current will flow in this ground loop