The impedance (Z) is a measure of opposition that a circuit to a current when a voltage is applied. The impedance extends the concept of resistance circuits alternating current (AC), and has both magnitude and phase, unlike resistance, which has only magnitude. When a circuit is powered with direct current (DC), there is no distinction between the impedance and resistance; the latter can be thought csa impedance with zero phase angle.

Closed circuit television, or CCTV (stands for closed circuit television) surveillance is a technology designed to monitor a variety of environments and activities. It is called closed, that, contrary to what happens with the media, all components are linked. In addition, unlike conventional television, this is a security system designed to