It is defined as the time rate of flow of electric charge through a cross-section of the conductor. The SI unit of electric current is ampere.
Hence, electric current = charge / time
Electric current is basically two types :
Direct Current : An electric current whose magnitude and direction do not change with time is called direct current. Its frequency is zero.
Alternating Current : An electric current whose magnitude change continuously and direction changes periodically is called alternating current. Its frequency is 50 Hz in India.
Conductor are the material through which electric charge can flow easily. e.g. Silver, iron, etc.
Insulator are the material through which electric charge cannot flows. e.g. Wood, rubber, etc.
Current Density The amount of current flowing through per unit area of cross-section of conductor provided the area in held in direction normal to current is known as current density.
\(j=\frac{i}{A}(A/M^ 2)\)
Ohm's Law According to this law, "the electric current
flowing through a conductor is directly proportional to the potential difference applied across its ends, provided the physical conditions remain unchanged.
V ∝ I ⇒ V = IR
The conductor which obey's Ohm's law are called ohmic conductor while the conductor in which Ohm's law is not valid are called non-Ohmic conductor.
Resistance is a property of conductor due to which it resists the flow of electric current through it. Its SI unit is ohm (2).
The resistance of conductor increases with increase the temperature but in the semiconductor, the resistance is decreases with increase the temperature.
Resistivity It is defined as the resistance of a conductor of unit length and unit area of cross-section.
R = ρ 1/A
where, ρ = resistivity of conductor.
Its SI unit is ohm-metre (Ω-m).
Conductance The reciprocal of resistance is known as conductance. Its SI unit is ohm-1(Ω-1)
G = 1/R
Specific Conductivity The reciprocal of resistivity is known as specific conductivity. Its SI unit is ohm-1 - m-1 (Ω-1 - m-1).
σ = 1/ρ
Combination of Resistors
