Theory

• An electric circuit consist of a load , conductors , and a power source .
• The polarity and the output voltage from a dc power source never changes direction . One terminal will be negative and other will be positive 
• According to the Electron current flow theory , electrons leave the negative terminal of the source , flow through the conductors and load(s) , and return to the positive terminal if the source 
• Direct current is used for electroplating , street trolley , and railway systems , or where a smooth and wide range of speed control is required for a motor driven application