Question

2.Explain the following: 
 ● Why is the tungsten used almost exclusively for filament of electric lamp?
 ● Why are the conductors of electric heating devices,such as bread toasters and electric irons,made of an alloy rather than a pure metal?
 ● Why is the series arrangement not used for domestic circuits?
● How does the resistance of a wire vary with its area of cross section?
● Why are copper and aluminium wires usually employed for electricity transmission?

Answer 1

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a) The melting point and resistivity of tungsten are very high. It does not burn very esay at a high temperature. The electric lamps glow at very high temperatures. Hence, tungsten is mainly used as heating element of electric bulbs.

b) The conductors of electric heating devices such as bread toasters and electric irons are made of alloy because resistivity of an alloy is more than that of metals. It produces large amount of heat and do not burn easily.

c) series arrangement is not used in domestic circuits. Because

◾ There is voltage division in series circuits. Each component of a series circuit receives a small voltage for a large supply voltage. As a result, the amount of current decreases and the device becomes hot.

d) Resistance (R) of a wire is inversely proportional to its area of cross-section (A):

R∝1 / A

e)

◾ Copper and aluminium wires have low resistivity.

◾ They are good conductors of electricity. Hence, they are usually employed for electricity transmission.

I hope, this will help you

Thank you____❤

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Answer 2

Answer:

(a) Tungsten is an alloy which has very high melting point and very high resistivity so does not burn easily at a high temperature.

(b) The conductors of electric heating devices such as bread toasters and electric irons are made of alloy because resistivity of an alloy is more than that of metals which produces large amount of heat.

(c) In series circuits voltage is divided. Each component of a series circuit receives a small voltage so the amount of current decreases and the device becomes hot and does not work properly. Hence, series arrangement is not used in domestic circuits.

(d) Resistance (R) of a wire is inversely proportional to its area of cross-section (A), i.e. when area of cross section increases the resistance decreases or vice versa.

(e) Copper and aluminium are good conductors of electricity also they have low resistivity. So they are usually used for electricity transmission.

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