Question

Which is the material used for filament of an electric bulb?
A) Tungsten
B) Nichrome
C) Copper
D) Cadmium

Answer 1

Hint:
In order to use the material for the filament of an electric bulb, some properties should be there in the material chosen. Some of these properties are:
1. Melting Point
2. Cost of material
3. Electrical Resistivity
4. Tensile Strength
Considering these properties, the material for the filament of the bulb is chosen.
Complete step by step answer:
Step I: The material chosen should have a high melting point. If a large amount of current is passed due to the ‘Heating Effect of Electric Current’ through the filament, then it will not oxidize easily. So the hotter, the filament gets without melting or oxidizing, the brighter will it glow.
Step II: Apart from that, the material should be chosen such that it should be cost effective, easily available and inexpensive.
Step III: In order to glow brighter without heating, the resistance provided by the material to the flow of current should be small or negligible so that maximum current can flow. Resistance is directly proportional to resistivity. So its electrical resistivity should be small.
Step IV: The material should have a high tensile strength. It means that the material should be able to take maximum load without melting or getting damaged.
All these properties are there in Tungsten. Also it is an alloy. So it has High melting point, low resistivity and very high tensile strength of all the metals.
Option A is the correct answer.

Note: There are other factors also that should be taken care of while choosing material for filament of electric bulbs. These are thermal conductivity, boiling point, vapor pressure of the material used.