The doc contains revision notes on kinematics. reference frame in which newtonian mechanics holds are called inertial reference frames or inertial frames. reference frame in which newtonian mechanics does not hold are called non-inertial reference frames or non-inertial frames.
Electric current is the continuous flow of electrons through a conducting material (like a copper wire). electrons are invisible so to understand the basics of how circuits work, it helps to examine a mechanical system that behaves in many ways similar to the electric circuit. this mechanical system consists of a pump pushing water through a closed pipe. if we imagine that the electrical current is similar to the water flowing through the pipe, then the following parts of the two systems are related: the pipe is the counterpart of the wire in the electric circuit the pump is the mechanical counterpart of the battery. the pressure generated by the pump, that drives the water through the pipe, is like the voltage generated by the battery to drive the electrons through the circuit. the seashells plug up the pipe and constrict the flow of the water creating a pressure difference from one end to the other. in a similar manner the resistance in the electric circuit resists the flow of electricity and creates a voltage drop from one end to the other. energy is lost across the resistor and shows up as heat. the power in the circuit is given by the product of the voltage and the current. the same power can be carried by a high voltage and a low current as is carried by a low voltage and a high current. the higher the current flow however, the more energy is lost through heating the wires when traversing the circuit. that's why high voltage and low current is used when transporting electrical energy along power lines.
This note explains the concept and working of p-n junction diode. the p-n junction is a versatile element, which can be used as a rectifier, as an isolation structure and as a voltage-dependent capacitor.