Electrical Resistivity and Conductivity

Electric current flows charged particles, typically electrons, through a wire or space in an electric field. The SI unit of electric charge is the coulomb. The SI unit of electric current, the ampere (A), was defined in 1835 by André-Marie Ampère as one joule per second. It should not be confused with the electrical current that can produce power from direct conversion into mechanical energy. The derived SI unit for the charge “q” is the coulomb (C). 

Electric current

“Electric current is defined as the flow of electric charge.” 

Electric current is the flow of electrons through a conductor. The magnitude of the electric current is defined as the difference in electric potential across two points in space: voltage. The maximum current that can flow in a resistive circuit with zero power dissipation is called the critical current and is equal to 50% of the character breakdown of insulation resistance (RA). Therefore, it is also called the critical current, the characteristic current and the breakdown current.

For direct current, the direction of electric current is defined by the direction of movement of electrons. For example, if a p-type semiconductor has more holes than electrons, holes move from the n-type semiconductor (with excess electrons) to it and carry a positive electric charge. This is called “holes moving into a positive terminal.” It defines positive current in an n-p junction device. Similarly, electrons move from an n-type semiconductor to a p-type terminal, and a positive current is defined.

The direction of electric current can be defined relative to the movement of charge carriers in a conductor. For example, an inductive circuit consists of an electrically conducting path through which charge carriers flow. For a steady current, the direction of current flow is defined as the direction in which positive charge carriers are moving. Conversely, for a steady flow of negative charge carriers, it is the direction opposite to them.

Electric current has several physical properties similar to those of a fluid. Therefore, electric currents can be described using the same equations for fluid flow. The interpretation of electric currents and electric potential differences in fluid flow is discussed in greater detail about Ohm’s law.

Electric charge

The charge that causes a current to flow through a conducting path is called an electric charge. Electric charges can be moving or stationary. For an electric charge to move along a conductor, it must accelerate or slow down by friction. If it moves slower than the speed of light in a vacuum, it must move laterally in space (either flowing along with the conductor or circulating within some magnetic field). The actual movement of an electric charge is called charge flow.

In some cases, only the direction and not the speed is relevant (for example, a current in a wire). The magnitude of the electric charge that causes a current to flow through a conductor is defined as the electric charge. However, this definition is often imprecise due to the kinetic energy of charges.

The resistance of a conductor depends on the length and cross-section of the conductor but is generally reasonably linear. For this reason, the resistance in many simple electronic circuits is specified as a constant rather than as a function of the current. A few examples are: simple electronic devices such as fixed resistors, potentiometers and light-dependent resistors are made with a fixed resistance. In addition, individual cells in a battery have internal resistance, but this has little effect on the overall circuit performance.

In older literature, the symbol was “r”, but it is now more common to use the letter R.

The constant “R” has units of ohms (Ω), watts (W) or milliohms (mΩ). The constant “k” has units of Joules/metre.

How fast do electrons travel in a straight line?

Some free electrons move at random velocity in materials that lead like metal above absolute zero temperature. Electrons tend to gravitate toward the positive potential when a potential is applied to a conductor. They will eventually collide with atoms and some of their kinetic energy will be lost. Electrons will continue to accelerate due to the electric field, as will random collisions with atoms. Nonetheless, because the electrons’ speed increment is in an equivalent bearing, their net speed will be in a comparative course.

Conclusion

Electric charge is the movement of positive or negative electrons across a conductor.

Electric current is the flow of electric charge through a circuit.

Depending upon the configuration of active components and resistors in a circuit, an electric current through the circuit will have different effects. For example, if a current is directed into a linear amplifier, it will cause the charge stored within its capacitors to be supplied to its output as an amplified signal. However, if a current is directed into a non-linear amplifier or comparator, it can cause transistors to switch states and change output voltage levels.