A diagram illustrating the passive sign convention, the standard convention used for defining power flow in an electrical component.    To comply with this convention, the direction of the voltage v and current i variables in an electric component must be defined as shown in the diagram, so that conventional current flows through the device from the positive voltage terminal to the negative.  With this convention, positive power flow p (big arrow) will represent power dissipated in the device.   So in a passive (load) component, such as a light bulb or appliance, power dissipation p = iv and electrical resistance R = v / i will be positive, while in an active (source) component, such as a battery or electric generator, power dissipation and resistance will be negative.
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Chetvorno