Explain the following :
(a) Why is tungsten used almost exclusively for filament of incandescent lamp ?
(b) Why are the conductors of electric heating devices, such as toaster 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 cross-sectional area ?
(e ) Why are copper and aluminium wires usually employed for electricity transmission.

Explanation

### Step-by-Step Text Solution:

#### (a) Why is tungsten used almost exclusively for the filament of incandescent lamps?
Tungsten is used for the filament of incandescent lamps primarily due to its high melting point, which is around 3422°C (6192°F). This allows tungsten to withstand high temperatures without melting when electric current passes through it. When heated, tungsten emits a bright light, making it ideal for lighting applications. Additionally, tungsten has a low vapor pressure at high temperatures, which means it does not evaporate quickly, prolonging the life of the filament.

**Hint:** Consider the properties of materials that allow them to withstand high temperatures and emit light effectively.

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