In this video, the author is explaining about Kirchhoff’s Voltage Law (KVL).
Kirchhoff’s Voltage Law (KVL) and Kirchhoff’s Current Law (KCL) are very fundamental laws in the electrical circuit. Using these laws we can find the voltage and current in any electrical circuit.
According to Kirchhoff’s Voltage Law, The algebraic sum of all the branch voltages around any close loop in the network is zero. So, if we move around any close loop in an electrical circuit and add the voltages across each element that we come across, then their algebraic sum is zero.
The sign convention for Kirchhoff’s Voltage Law:
While moving around the loop, if we are moving from negative to the positive potential, or there is a rise in potential then that voltage can be considered as a positive voltage. Likewise, if we are moving from positive to negative potential across any element, or there is a drop in potential then that voltage can be considered as a negative voltage.
It is not necessary to follow the same convention. One can follow the other way around too and can still solve the problems, but whatever sign convention you choose, stick to the same sign convention.
Courtesy: ALL ABOUT ELECTRONICS