Physics The electric current &Ohm's law review

Physics| The electric current &Ohm's law - review
The electric current &Ohm's law (review)

The electric current:It is the flow of electric charges through a conductor The electric current intensity (I) it is the quantity of electricity in coulombs passing through a given cross-sectional area in one second.



The direction of the electric current:The traditional current(the motion of positive charges) outside the source, it is from the positive pole to the negative one in the electric circuit. The real current (the motion of negative charges): it is from negative pole to positive one in the electric circuit. The electric current intensity is measured in Ampere, mille Ampere or micro Ampere.

One Ampere:It is the electric current intensity when a quantity of electricity of one coulomb passes through a given cross- sectional area of a conductor in one second. the electric current intensity is measured by Ammeteror mille Ammeter or micro Ammeter.



One coulomb:It is the quantity of charge passing through a given cross-sectional area in one second. When the electric current intensity is one Ampere.
The electric current passes in a conductor between two points under effect of potential difference.

The potential difference between two points(V):It is the work done (in joule) to transfer a quantity of electricity of one coulomb from one point to another.



The electromotive force of a source (E.M.F.):The total work done to transfer a unit charge of one coulomb through the whole electric circuit. It is measured in volts.


The electric current &Ohm's law (review)

Ohm's law:At constant temperature, the current produced in a given conductor is directly proportional to the electric potential difference across its terminals.



Resistance:it is the opposition for electric current to flow , the potential difference must be great enough to overcome the resistance of the path.

The resistance of a conductor (R):The ratio of potential difference to the electric current flowing through a conductor.

The ohm:The resistance of a conductor when the potential difference across its terminals is one volt and the current passes through it is one ampere.



Parameters affecting the electric resistance:
1 – The length of conductor (L).
2 – The cross sectional area of the conductor (A).
3 – The kind of the material of the conductor.
4 – The temperature of the conductor.

The resistivity of a material (ρe):It is numerically equal to the resistance of a conductor of 1 m long and 1m2 in cross sectional area, and it is a physical property of this material.

The electrical conductivity (σ ):It is reciprocal of the resistivity of a materialOR, it is the reciprocal of the resistance of a conductor of length 1m and cross sectional area 1m2 and is measured in ohm-1 m-1 or Simon m-1

The electromotive force of a cell (E.M.F.):The electric potential difference between the two poles of the battery when the elec. circuit is opened.