Current Electricity Basics
* Electric current is uniform flow of charges in a particular direction.
* The rate of flow of charge or uniform motion of electrons:
( I = Q/t)
* Potential difference is the work done in moving a unit charge between two points in an electric field against the direction of force:
( V =W/Q)
* Electric resistance is the opposition to the flow of electrons by the conductor.
Factors affecting electric resistance are:
* The length of the conductor
* The cross sectional area of the conductor
* The resistivity of conductor material
* The temperature of the conductor
Thus, ( R = p(1/A))
* Resistivity of a material is the resistance offered by a conductor having unit length and unit area of cross section.
* Ohm’s law states that the current passing through a conductor is:
* Directly proportional to the voltage in the conductor and
* Inversely proportional to the resistance of the conductor
Thus, I = v/r
Current Electricity Circuits
* In parallel circuits:
V = V1 = V2 = V3
Itotal = I1 + I2 + I3
1/Req = 1/R1 + 1/R2 + 1/R3
Heating Effect of Electric Current
* Heating effect of electricity: when current passes through a conductor, the conductor gets heated as electric energy is converted into heat energy.
* A good heating element should have high resistivity, a high melting point and should show negligible variation in resistance due to temperature changes.
* An electric fuse is used to break the flow of electric current when the device is over loaded. Its mechanism is based on the heating effect of electricity.
* Joule’s law: The amount of heat produced in a conductor is equal to the product of the amount of current squared, the resistance of the conductor, and the time for which current passes through the conductor.
Thus, H = i2Rt