Question

Explain the following.
(a) Why is the 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?

Answer 1

Filament is the part of the light bulb which glows when current passes through it.
A homogeneous mixture of two or more metals with or without small quantities of non-metals is called an alloy.

Complete step by step solution:
Part (a):
The metal tungsten is almost exclusively used for the filament of the electric lamp because it has a very high melting point due to which it does not melt even when it is heated to high temperatures due to the passage of electric current.

Part (b):
Conductors of electric heating devices, such as bread-toasters and electric irons are made of an alloy rather than pure metal due to the following two reasons:
1. The melting point of alloys is higher than their parent metals. Hence the electrical heating devices have a lower chance of melting due to overheating as alloys have a higher melting point than the pure metals of which it is made of.
2. Alloys are way more corrosion resistant than their parent metals. Hence the electrical heating devices have a lower chance of corrosion if they are made of alloys rather than pure metals.

Part (c):
Series arrangement is not used for domestic circuits due to the following reasons:
1. In a series connection, if one electrical appliance stops working, then all other appliances would also stop working.
2. In a series connection, all electrical appliances have a single switch due to which they cannot be turned on or off individually.
3. In a series connection, all the appliances do not get the same voltage as the voltage gets divided among the appliances.
4. In a series connection, the equivalent resistance due to all the appliances increases too much (as the current has a single path to flow) due to which the amount of current flowing becomes very small.

Hence, we use parallel connections instead of series connections for domestic circuits.

Part (d):
The resistance of the wire is inversely proportional to its cross-section area (i.e. resistance decreases with an increase in cross-section area of the wire).
$Resistance{\text{ }}\alpha {\text{ }}\dfrac{1}{{Cross - section{\text{ }}of{\text{ }}wire}}$

Part (e):
Copper and aluminum are employed for electricity transmission because they are not only cheap but also excellent conductors of electricity.

Note: Solving this type of question require in-depth knowledge of theoretical concepts.