ELECTRICAL QUANTITIES

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POTENTIAL

Potential refers to the possibility of doing work

Any charge has the potential to do the work of moving another charge, by either attraction or repulsion. When we consider two unlike charge, they have a difference of, potential. The charge has a certain amount of potential, corresponding to the amount of work this charge can do.

UNIT

The unit of potential difference is volt named after Alessandro Volta. The volt is the measure of work needed to move an electric charge.

VOLT

One volt is the potential difference (voltage) between two points when one joule of energy is used to move one coulomb of charge from one point to the other

OR

Potential difference is one volt if 0.7376 (foot-pound) of work is required to move 6.25 x 1018 electrons.

Since

6.25x 1018 electrons = l coulomb

0.7376 foot-pound = 1 joule

Hence definition will be:

One volt is equal to one joule of work per coulomb of charge (V = W/Q)

Its symbol is V.


CURRENT

The continuous motion of free electrons by applying potential difference is called current.

OR

Electrical current is defined as the rate of flow of electrons in a conductive or semi-conductive Material.

I = Q/t

Current

Free electrons are available in all conductive and semi-conductive materials. These electrons drift randomly in all directions, from atom to atom, within the structure of the material. Now if a voltage is placed across. The conductive or semi-conductive material, one end becomes positive and the other end negative as indicated in figure. The repulsive force between the negative voltages at the left end causes the free electrons (negative charges) to move toward the right. The attractive force between the positive voltage at the right end pulls the free electrons from the negative end of the material to the positive end, as shown in figure.

Current

The movement of the free electrons from the negative end of the material to the positive end is the electrical current, symbolized by I

UNIT

The unit of current is Ampere symbolized by A it is named after Andre Ampere

AMPERE

The amount of current is one ampere if 6.25x1018 electrons move per second.

OR

The amount of current is one Ampere if one coulomb (1c) of charge flows through a conductor for one second.


RESISTANCE

Resistance is the blocking of free electrons while moving through a conductor.

OR

The opposition that limits the amount of current produced by applied voltage is called resistance.

When current flows in a material and occasionally collide with atoms. These collisions cause the electrons to lose some of their energy and thus their movement is restricted. The more collisions, more the flow of electrons is restricted. This restriction varies and is determined by the type of material. The property of a material that restricts the flow of electrons is called resistance designated R.

UNIT

Resistance R, is expressed in the unit of Ohm, named after George Simon Ohm and symbolized by the Greek letter Omega (CI).

OHM

Ohm is defined as:

There is one Ohm (10) of resistance when one Ampere (1A) of current flows in a material with one volt (1V) applied.

OR

The resistance in which steady current of one Ampere generates heat of 1 joule per second.

OR

A resistance that develops 0.24 calorie of heat by currents for one second has one Ohm resistance


Difference between conventional current and electron current

CONVENTIONAL CURRENT

The motion of positive charges, in the opposite direction of the flow of electrons is called conventional current.

This direction is generally used for analyzed circuit in electrical engineering. The reason is based on some traditional definitions in the science of physics. By the definitions of force and work with positive values, positive potential is considered above the negative potential. Conventional current corresponds to a motion of positive charges (Falling down hill) from positive to a negative potential.

An example of positive charges in motion for conventional current is the current of whole charges in P-type semi-conductor. Also a current of positive ions in liquids and gasses moves in opposite direction of electron flow.

ELECTRON CURRENT

The current which is due to the motion of electrons only in the opposite direction of conventional current is called electron current.

The direction of electron drift for current I is out from negative side of the voltage source, current I passes through external circuit with R and returns to positive side of voltage source.

Inside the battery, the electron moves towards the negative terminal to produce potential difference. The battery is doing work of separation of negative and positive charges, accumulated electrons at negative terminal and protons at positive terminal. The potential difference allows electrons to move from negative terminal passes through external circuit, returns to positive terminal.

However the direction of electron or electronics current flow is from negative potential to positive potential 

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