Electricity — Ohm’s Law — Resistance and Resistivity ( Part 3 )
Ohm’s Law
Ohm’s Law tells Relationship between Electric Current and Potential Difference ( Voltage ).
If the potential difference doubled, the current gets doubled.
If the potential difference is halved, the current also gets halved.
Relationship between Current and Voltage
According to Ohm’s Law , Current is directly proportional to potential difference ( Voltage )
The symbol used to denote the proportionality is ’∝’
Resistance
R is Proportionality Constant called Resistance.
Ratio of Voltage to Current is called Resistance.
Resistance is the physical property of object which opposes flow of Current through it.
SI unit of Resistance is ohm represented by a Greek symbol Ω
Voltage — Current Graph
Slope of Voltage — Current Graph is always a Straight Line
Slope of Voltage — Current Graph gives Resistance
Formulae — based on — Ohm’s Law
Calculate Potential Difference ( V )
Calculate Current ( I )
Current is directly proportional to Potential Difference.
Current is inversely proportional to resistance
If the resistance is doubled, the current gets halved
If the resistance is halved, the current gets doubled
Electric Current depends on Potential Difference and Resistance.
1 ohm is the resistance of a conductor such that when a potential difference of 1 volt is applied to its ends, a current of 1 ampere flows through it.
Calculate Resistance ( R )
1 ohm is the resistance of a conductor such that when a potential difference of 1 volt is applied to its ends, a current of 1 ampere flows through it.
When Electrons flow , they collide with other Electrons and Atoms in the Conductor that causes some Obstruction or Opposition to flow of Electric Current in the Conductor.
Resistance is a measure of the opposition to current flow in an electrical circuit
Factors affecting Resistance
The physical property of a conductor due to which it opposes the flow of current through it is called Resistance.
Resistance of a conductor depends on — Length, Thickness, Nature of material and Temperature of the Conductor
Length
Resistance is directly proportional to the Length.
when the length of a wire is doubled, its resistance also gets doubled;
When the length of a wire is halved, then its resistance also gets halved.
Cross Sectional Area
Resistance is inversely proportional to the cross-sectional area.
When cross-sectional area of a wire is doubled, its resistance gets halved
When cross-sectional area of wire is halved, its resistance will get doubled.
Diameter
Thick wire has less resistance.
Thin wire has more resistance.
The thickness of a wire is usually represented by its diameter.
Resistance of a wire is inversely proportional to the square of its diameter
when the diameter of a wire is doubled , its resistance becomes one-fourth.
when the diameter of a wire is halved, its resistance becomes 4 times.
Temperature
Resistance is directly proportional to Temperature.
Resistivity
Resistivity is the characteristic property of the material by which it opposes the amount of current through it.
The Resistance of material having unit length and unit cross-sectional area is known as its specific resistance or resistivity.
Resistivity of a substance is numerically equal to the resistance of a rod of that substance which is 1 metre long and 1 square metre in cross-section
Resistivity value of specific material remains Constant even if there is change in Length and Cross Sectional Area of object made up of given material.
The resistivity is denoted by the symbol ρ and is measured in Ohm-metre symbolically represented as Ω-m
Relationship between Resistance and Resistivity
Resistivity is only proportional to the Nature and Temperature of the particular material
Conductors / Resistors / Insulators
Those substances which have very low electrical resistance are called good Conductors.
Silver metal is the best conductor of electricity
Those substances which have comparatively high electrical resistance, are called Resistors
Those substances which have infinitely high electrical resistance are called Insulators
