There are two quantities that we are like to keep track of in electronic circuit :voltage and current .The voltage is also called potential difference or electromotive force . The unit of measure is volt , with voltages usually expressed in volts (V) ,kilovolts (kV) , millivolts (mV) , or microvolts (μV).
Current is the rate of flow of electric charge passing a point . The unit of measure is the ampere , or amp ,with currents usually expressed in amperes (A) ,milliamperes (mA) ,microamperes (μA) ,nanoamperes (nA) ,or occasionally picoamperes (pA) .By convention , current in a circuit is considered to flow from a more positive point to a more negative point , even though the actual electron flow is in the opposite direction .
Here are some simple rules about voltage , current and power :
The sum of the currents into a point in a circuit equals the sum of the currents out . This is sometimes called Kirchoff’s current law .Generally engineers refer to such a point as a node . From this ,we get the following : for a series circuit the current is the same .
