Electricity:Resistance

Recap:Last time we have tackled about

electricity . Again… A type of energy fueled by the transfer of electrons from positive and negative points within a conductor.

Electricity is widely used for providing power to buildings, electric devices, and even some automobiles…

Electricity is very harmful to humans because of high voltage it contains but electricity can be lessened by the use of Resistors with different resistance…

ResistanceResistance of an object to the flow of

electrical current.R = V/IResistance equals the ratio of voltage to

current.Unit: Ohm ( Ω )An object of uniform cross section has a

resistance proportional to its resistivity and length and inversely proportional to its cross-sectional area.

Georg Ohm and Ohm’s LawGeorg Simon Ohm (1789 - 1854) first investigated the relationship between the current in an electric circuit element and the electrical potential difference, often called voltage, across the circuit element.

Ohm's LawFor a circuit or circuit element, Ohm's law mathematically relates the current, the voltage, and the electrical resistance. The voltage is more properly called the electrical potential difference, but voltage is often used because it is less of a mouthful.Ohm found that in a circuit the voltage and current are directly proportional to each other. That means if the current, I, in a circuit is plotted along the horizontal, or x, axis and the voltage, V, is plotted along the vertical, or y, axis, then the result will be a straight line. The slope of this line is the resistance, R, of the circuit.

ResistorsA resistor is a two-terminal electronic component that produces a voltage across its terminals that is proportional to the electric current through it in accordance with Ohm's law:

V = IR

Resistors are elements of electrical networks and are ubiquitous in most electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire. The primary characteristics of a resistor are the resistance, the tolerance, the maximum working voltage and the power rating. 

ConductorsA conductor is a material which contains movable electric charges. In metallic conductors, such as copper or aluminum, the movable charged particles are electrons. Positive charges may also be mobile in the form of atoms in a lattice that are missing electrons (known as holes), or in the form of ions, such as in the electrolyte of a battery. Insulators are non-conducting materials with fewer mobile charges, which resist the flow of electric current.

All conductors contain electric charges which will move when an electric potential difference (measured in volts) is applied across separate points on the material. This flow of charge (measured in amperes) is what is meant by electric current. In most materials, the direct current is proportional to the voltage (as determined by Ohm's law), provided the temperature remains constant and the material remains in the same shape and state.

In Metals

A metal consists of a lattice of atoms, each with a shell of electrons. This is also known as a positive ionic lattice. The outer electrons are free to dissociate from their parent atoms and travel through the lattice, creating a 'sea' of electrons, making the metal a conductor. When an electrical potential difference (a voltage) is applied across the metal, the electrons drift from one end of the conductor to the other under the influence of the electric field.

In metals, the Fermi level lies in the conduction band giving rise to free conduction electrons. However, in semiconductors the position of the Fermi level is within the band gap, approximately half-way between the conduction band minimum and valence band maximum for intrinsic (semiconductors. This means that at 0 kelvins, there are no free conduction electrons and the resistance is infinite. However, the resistance will continue to decrease as the charge carrier density in the conduction band increases.

In Insulators

In liquids/electrolytes

In electrolytes, electrical conduction happens not by band electrons or holes, but by full atomic species (ions) traveling, each carrying an electrical charge. The resistivity of ionic liquids varies tremendously by the concentration - while distilled water is almost an insulator, salt water is a very efficient electrical conductor. In biological membranes, currents are carried by ionic salts. Small holes in the membranes, called ion channels, are selective to specific ions and determine the membrane resistance.

Direct Current and

Alternating Current

Difference between an Alternating Current and Direct CurrentAlternating Current Direct Current

In alternating current (AC) the movement of electric charge periodically reverses direction. AC is the form in which electric power is delivered to businesses and residences. The usual waveform of an AC power circuit is a sine wave.

Direct current (DC) is the undirectional flow of electric charge. The electric charge flows in a constant direction, distinguishing it from alternating current (AC).

The First Direct CurrentElectricity is a very different energy source

than heat or light. In nature, electricity only rarely occurs, in some animals or with lightning. In the search to create electrical energy, scientists discovered that electrical and magnetic fields are related. A magnetic field near a wire causes electrons to flow in a single direction along the wire because they are repelled and attracted by the north or south poles. Thus, DC power from a battery was born, primarily attributed to Thomas Edison's work and promotion.

The End!!!Thank You!!!