Q13 of 27 Page 1

A. List the factors on which the resistance of a conductor in the shape of a wire depends.

B. Why are metals good conductors of electricity whereas glass is a bad conductor of electricity? Give reason.


A. The resistance of a wire depends mainly on three factors:


(a) It is directly proportional to the length of the wire, R ∝ l


(b) It is inversely proportional to the cross-sectional area of the wire, R ∝


(c) It depends upon the material out of which the wire is made, which is called the resistivity of the wire.


(d) Resistance of a wire also varies with temperature.


The relationship of wire with these aforementioned factors can be mathematically expressed in the following way,



Where ρ is the resistivity of the wire, A is the cross-sectional area of wire and l is the length of the wire.


B. Metals are considered as a good conductor of electricity as they contain delocalised electrons that are not firmly held by the atom. Instead, they can move freely through the positive metal ions. When a potential difference is applied across the metal, the electrons are pushed away towards the positive terminal of the cell, away from the negative terminal of the battery. On the other hand, glass is a poor conductor of electricity as it contains no loosely bound free electrons. Consequently, glass being an insulator is incapable of conducting electricity.


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