Electric Current And Related Parameters Chapter 12 Electric Current And Related Parameters

Engineers understand the importance of electricity and electrical power and the role they play in our everyday lives. As future engineers you should know what is meant by: voltage, electric current, And the difference between direct and alternating current. You should also know the various sources of electricity and understand how electricity is generated

The ampere is defined as that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed 1 meter apart in a vacuum, would produce between these conductors a force equal to 2x 10-7 Newton per meter of length. In SI units, the unit of charge is the coulomb (C). One coulomb is defined as the amount of charge that passes a point in a wire in 1 second when a current of 1 ampere is flowing through the wire.

The electric force exerted by one point charge on another is proportional to the magnitude of each charge and is inversely proportional to the square of the distance between the point charges. Moreover, the electric force is attractive if the charges have opposite signs, and it is repulsive if the charges have the same sign. The electric force between two point charges is given by Coulomb’s law

Voltage Voltage represents the amount of work required to move charge between two points, and Current represents the amount of charge that is moving between the two points per unit time. Electromotive force (emf ) represents the electric potential difference between an area with an excess of free electrons (negative charge) and an area with an electron deficit (positive charge). The most common sources of electricity are chemical reaction, light, and magnetism. Batteries In all batteries, electricity is produced by the chemical reaction that takes place within the battery.

To increase the voltage output, batteries are often placed in a series arrangement connected in a parallel arrangement, produce the same voltage, but more current.

Power Plants Electricity that is consumed at homes, schools, malls, and by various industries is generated in a power plant. Water is used in all steam power-generating plants to produce electricity. A simple schematic of a power plant is shown in Figure 12.

Direct Current and Alternating Current1/2 Direct current (DC) is the flow of electric charge that occurs in one direction, as shown in Figure 12.4(a). Direct current is typically produced by batteries Direct current was not economically feasible to transform because of the high voltages needed for long-distance transmission

Direct Current and Alternating Current2/2 Alternating current (AC) is the flow of electric charge that periodically reverses. The magnitude of the current starts from zero, increases to a maximum value, and then decreases to zero. This flow pattern is repeated in a cyclic manner. The time interval between the peak value of the current on two successive cycles is called the period, and the number of cycles per second is called the frequency. The peak (maximum) value of the alternating current in either direction is called the amplitude. Alternating current is created by generators at power plants. The current drawn by various electrical devices at your home is alternating current. The alternating current in domestic and commercial power use is 50 cycles per second (hertz).

Kirchhoff’s Current Law The law states that at any given time, the sum of the currents entering a node must be equal to the sum of the current leaving the node

Electrical Circuits and Components An electrical circuit refers to the combination of various electrical components that are connected together. Examples of electrical components include wires (conductors), switches, outlets, resistors, and capacitors.

Circuit Connections: Electrical components can be connected in either a series or a parallel arrangement. Series Circuit: Similar to a constant flow of water in a series of pipes of varying size, the electric current flowing through a series of elements in an electric circuit is the same (constant). For a circuit that has elements in a series arrangement, the following is true: • The voltage drop across each element can be determined using Ohm’s law. • The sum of the voltage drop across each element is equal to the total voltage supplied to the circuit. • The total resistance is the sum of resistance in the circuit.

one current and v=v1+v2+v3

Parallel Circuit Consider the circuit shown in Figure below. The resistive elements in the given circuit are connected in a parallel arrangement. For this situation, the electric current is divided among each branch. One volt, I=I1+I2+I3