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



It depends upon following factors

Length of Conductor


Resistance of a conductor is directly proportional to its length

R ∝ l


if we increase the length of a wire (conductor),its resistance increases(and hence less current can pass through it)

If we reduce length,resistance decreases (and hence more current can pass through it)


Area of Cross Section




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


Due to the presence of free electrons and low resistivity , metals are good conductors of electricity. 

Due to the absence of free electrons and high resistivity, glass is a bad conductor of electricity.


(c) Why are alloys commonly used in electrical heating devices? Give reason.



The heating element of an electric heater is made up of alloys because

Alloys have very high resistance, so when the current passes through the alloy, it offers great resistance.

The high resistance produces heat, which is required in such appliances.

If the heating elements were made of pure metal, they would have low resistance.

So, they will pass all the current flowing through it and hence would not produce heat.

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CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo