ii.1. Electric Current: A Fundamental Force in Modern Technology

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ii.1. Electric Current: A Fundamental Force in Modern Technology

Electric current is the flow of electric charge through a conductor. It is a fundamental concept in physics and a cornerstone of electrical engineering. Currents have diverse applications, from powering household appliances to driving complex electronic systems, making them essential in modern technology.

Electric Current Made Simple: Understanding Charge Flow and Ampere Units	Meaning: Electric current is expressed by the amount of charge (electrons) flowing through a particular area in unit time. In other words, it is the rate of flow of electric charges. The source can be through inverters, a battery, generators etc. and can be used for lighting, heating, cooling and so on. Flow of Current: Electric current was considered to be the flow of positive charges and the direction of flow of positive charges was taken to be the direction of electric current. Opposite: Conventionally, in an electric circuit the direction of current is taken as opposite to the direction of the flow of electrons (negative charges). Therefore, if a net charge Q, flows across any cross-section of a conductor in time t, then the current I, through the cross-section is, I = Qt Unit: The SI unit of electric charge is coulomb (C), which is equivalent to the charge contained in nearly 6 × 1018 electrons. An electron possesses a negative charge of 1.6 × 10–19 C. [A schematic diagram of an electric circuit] The electric current is expressed by a unit called ampere (A), named after the French scientist, Andre-Marie Ampere (1775–1836). One ampere: It is constituted by the flow of one coulomb of charge per second, i.e. 1A = 1C1s Small quantities of current are expressed in milliampere (1 mA = 10–3 A) or in microampere (1 µA = 10–6 A).
Electric Circuits: The Journey of Electric Current from Cells to Bulbs	Definition: A continuous and closed path of an electric current is called an electric circuit. Electric circuit is the complete path for electricity to pass, from one terminal of the electric cell through the bulb and back to the other terminal of the electric cell. The bulb glows only when current flows through the circuit. Sometimes an electric bulb does not glow even if it is connected to the cell. This may happen if the bulb has fused. One reason for a bulb to fuse is a break in its filament. If the filament of the bulb is broken, the path of the current between the terminals of the electric cell is not completed and hence the current cannot flow.
Circuit Diagram	It is a diagram, in which different components of the circuit are represented by the symbols. Circuit diagrams are much easier to draw using symbols. A Circuit diagram when switch is ON
Electric Potential and Potential Difference	Potential Difference: For flow of charges in a conducting metallic wire, gravity has no role to play, the electrons move only if there is a difference of electric pressure called the potential difference along the conductor. This difference of potential may be produced by a battery, consisting of electric cells. The chemical action within a cell generates the potential difference across the terminals of the cell, even when no current is drawn from it. When the cell is connected to a conducting circuit element, the potential difference sets the charges in motion in the conductor and produces an electric current. In order to maintain the current in a given electric circuit, the cell has to expend its chemical energy stored in it. Thus, the electric potential difference between two points in an electric circuit carrying some current as the work done to move a unit charge from one point to the other Potential difference (V) between two points = Work done (W) / Charge (Q) V = W/Q The SI unit of electric potential difference is volt (V), named after Alessandro Volta (1745 –1827), an Italian physicist. One volt: One volt is the potential difference between two points in a current carrying conductor when 1 joule of work is done to move a charge of 1 coulomb from one point to the other. Therefore, 1 volt = 1 joule/ 1 coulomb 1 V = 1 J C–1

Flow of charges inside a wire

Inside the solid, the atoms are packed together with very little spacing between them.
But the electrons can travel through a perfect solid crystal smoothly and easily, almost as if they were in a vacuum.
The ‘motion’ of electrons in a conductor, however, is very different from that of charges in empty space.
When a steady current flows through a conductor, the electrons in it move with a certain average ‘drift speed’.
One can calculate this drift speed of electrons for a typical copper wire carrying a small current, and it is found to be actually very small, of the order of 1 mm/s.
The physical drift of electrons in the conducting wires is a very slow process. The exact mechanism of the current flow, which takes place with a speed close to the speed of light, is fascinating.