A stream of electrons moving through a conductor constitutes an electric current. Conventionally, the direction of current is taken opposite to the direction of flow of electrons. The SI unit of electric current is ampere.
To set the electrons in motion in an electric circuit, we use a cell or a battery. A cell generates a potential difference across its terminals. It is measured in volts (V).
Resistance is a property that resists the flow of electrons in a conductor. It controls the magnitude of the current. The SI unit of resistance is ohm (Ω).
Ohm’s law: The potential difference across the ends of a resistor is directly proportional to the current through it, provided its temperature remains the same.
The resistance of a conductor depends directly on its length, inversely on its area of cross-section, and also on the material of the conductor. The equivalent resistance of several resistors in series is equal to the sum of their individual resistances.
The electrical energy dissipated in a resistor is given by W = V × I × t
The unit of power is watt (W). One watt of power is consumed when 1 A of current flows at a potential difference of 1 V.
The commercial unit of electrical energy is kilowatt hour (kWh). 1 kW h = 3.6 × 106 J.