(a) List the factors on which the resistance of a conductor in the shape of wire depends.
(b) Why are metals good conductor of electricity whereas glass is a bad conductor of electricity. Give reason.
(c) Why are alloys commonly used in electrical heating devices? Give reason.
Answers
Answer:
a) 1) Length of the conductor. 2) Area and cross-section of the conductor. 3) Effect of the material of the conductor. 4) Effect of temperature on the material.
b) Metals are good conductor of electricity because they have very large number of free valance electrons whereas glass has no free electrons to conduct electricity. So metals good conductor whereas glass is a bad conductor of electricity.
c) Most electrical heating devices use alloys because they have high resistivity and the melting point is also high in them.
Required Answers :
Answer (A) :
Resistance of a conductor in the shape of a wire depends on the following factors:-
- It is directly proportional to the length of conductor (R∝L).
- It depends on nature of material of conductor.
- It depends on temperature of conductor where it is being used.
- It is inversely proportional to the area of cross-section of the conductor.
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Answer (B) :
Metals are good conductor of electricity because of their Lower resistivity.
Metals have resistivity of 10⁻⁸ to 10⁻⁶ Ωm. Hence, they provide less opposition to the flow of electric charges through them and hence they have higher conductivity.
Glass is a bad conductor of electricity as it has extremely high resistivity and hence provide greater opposition to flow of current or electrons. Hence they are in the group of insulators having resistivity of 10¹⁷ Ωm.
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Answer (C) :
Alloys are used in electrical heating devices as:
- They have higher resistivity than their constituent metals and they dessipates a lot of heat energy when current flows through it.
- They have high melting and boiling points. They don't get oxidised or burnt even at a very high temperature.