# . Explain the following

(a) Why is tungsten used almost exclusively for filament of electric lamps?

(b) Why are the conductors of electric heating devices, such as bread - toasters and electric irons, made of an alloy rather than a pure metal?

(c) Why is the series arrangement not used for domestic circuits?

(d) How does the resistance of a wire vary with its area of cross-section?

(e) Why are copper and aluminum wires usually employed for electricity transmission?

Explanation:

(a) Tungsten has a very high melting point due to which the filament made up of tungsten does not melt at very high temperatures.

(b) Alloy has more resistance than conductors. As electrical heating devices are required to produce a lot of heat they need to be made up of elements having high resistance. High resistance elements release a lot of heat as the loss in voltage due to the resistance of alloy gets converted to heat energy.

(c) The series arrangement is not used for domestic circuits because there is a loss in potential difference across the elements in a series arrangement due to which the power in the circuit will be less than the applied power and the farther the element is connected in the circuit, lesser the power supplied to that element.

(d) The resistance of a wire varies with its area of cross-section because according to the formula of resistance,R=Pl/A resistance is inversely proportional to the area of cross-section of the conductor.

(e) Copper and aluminum wires are usually employed for electricity transmission because they have low resistivity due to which there is less loss of power while transmitting the electricity.

(a) Tungsten is used almost exclusively for filament of electric lamps because it does not get destroyed at high temperatures.

(b) The conductors of electric heating devices, such as bread - toasters and electric irons are made of an alloy rather than a pure metal because alloys have more resistance.

(c) The series arrangement is not used for domestic circuits because uneven power is supplied in a series arrangement.

(d) The resistance of a wire varies with its area of cross-section because it is inversely proportional to the area of cross-section of the wire.

(e) Copper and aluminium wires are usually employed for electricity transmission because they have low resistivity.