Resistances of Different Materials

Introduction

Resistance is the property of materials which allow the electric current to flow. Resistance opposes the current flow. The unit of resistance is ohms denoted by the Greek omega Ω. The resistance depends on the voltage across a certain resistor and the current which flows through it. Resistance is a measure which opposes the current flow in a particular electric circuit. 

Electrical resistance of a body is the measure of opposition to the current flow. 

Electrical Resistance

When the flow of an electric current is through a bulb or a conductor, then then conductor offers some hindrance to the current and this hindrance is the electrical resistance which is denoted by R. Each material has an electrical resistance and thus the conductors give out heat if current passes through it.

Ohm’s law states that, the potential difference across the conductor is directly proportional to the conductor the current which flows through a conductor.

The mathematical form of Ohm’s law is given as

V I

V=IR

Therefore, Resistance is given as 

R=V/I

Here, 

V = potential difference

I = current

R = resistance

From the above equation, we conclude that the resistance is the ratio of potential difference across the conductor to the current flow through it.

Electric charge flows through some materials more easily than through others. Electrical resistance measures how much the flow of that electrical charge is restricted within a given circuit. 

Factors Affecting Electrical Resistance

The factors which affect the resistances are given below.

1. Electrical Resistance depends inversely on area of cross-section of conductor
2. Electrical Resistance depends directly on the length of conductor
3. Electrical Resistance also depends material of conductor
4. Temperature of conducting material is also one of the factors which affect the electrical resistance.

Now, from factors affecting resistance we have,

R=(L)/A

Here,

= resistivity

Electrical Conductance

The inverse resistance is known as the electrical conductance. Electrical conductance is the ease with which the flow of an electrical current takes place. It is denoted by G.

Therefore,

G=1/R

Hence,

G=I/V

Resistivity

Electrical resistivity is the electrical resistance per unit length and unit area of cross-section at a given temperature and is represented by ρ. Electrical resistance is also referred to as a specific electrical resistance. Electrical resistivity unit is ohm meter.

Resistivity Formula

The resistivity formula is used to determine the resistivity which is given as

= E/J

Here,

E = electric field (V/m)

J = Current density (A/m2)

Also from the resistance formula, we can determine the resistivity formula as

=(RA)/L

The resistance of thick wire decreases and it increases for the thin wire because the cross – sectional area is less for thin wire. The resistance of wire increases when the length of the wire is increased. The resistance of wire decreases when the length of the wire is decreased.

Resistivity of Various Materials

Material having high resistivity has high resistance and resist the flow of electrons. And the material with low resistivity has low resistance and therefore the electrons can flow smoothly through the material.

For example, the resistivity of copper and aluminium are low. Good conductors have lower resistivity. The resistivity of Insulators is high. The resistivity of semiconductors lies between the resistivity of conductors and the resistivity of insulators. Gold is a good conductor of electricity and thus gold has a low resistivity (specific resistance).

Glass is a good insulator that does not allow the flow of electrons. Therefore, it has a high specific resistance. Silicon is a semiconductor and therefore enables partial movements of electrons. The resistivity of silicon is between glass and gold. The specific resistance of a perfect conductor is zero (0) and infinite for a perfect insulator.

Conclusion

Resistance is the property of materials which allow the electric current to flow. Resistance opposes the current flow. The unit of resistance is ohms denoted by the Greek omega Ω.

Electric Current is defined as the rate of flow of electrons inside a conductor. Ampere is the SI Unit of electric current which is denoted by A.

The factors which affect the resistances are given below.

1. Electrical Resistance depends inversely on area of cross-section of conductor
2. Electrical Resistance depends directly on the length of conductor
3. Electrical Resistance also depends material of conductor
4. Temperature of conducting material is also one of the factors which affect the electrical resistance.

Electrical resistivity is the electrical resistance per unit length and unit area of cross-section at a given temperature and is represented by ρ.

Electrical resistivity unit is ohm meter.

The resistivity formula is used to determine the resistivity which is given as

=E/J

=(RA)/L

The inverse resistance is known as the electrical conductance.

G=1/R

G=I/V

Conductors are the materials which conduct electricity easily.