Question

Which of the following things can be used as filaments of electric bulbs?
A. Tungsten
B. Tin
C. Lead
D. Steel

Answer 1

Hint:Recall the basics of filament used in an electric bulb. Recall which conditions should be satisfied by the material to be used as filament in an electric bulb. Check which of the materials given in the options satisfy all these conditions and choose the correct option for the filament of the electric bulb.

Complete answer:
The conditions for a material to be used as filament in an electric bulb are as follows:
1. The material should have a very large melting point.
2. The material should have a high resistivity.
3. The material should have the ability to sustain at very high temperatures.
4. The material should not get oxidized easily at high temperatures.
5. The material can be drawn into a fine wire.

All these conditions are satisfied by only tungsten from all the material in the given options. Also the tungsten along with satisfying all the above conditions also is cheap as compared to the other materials that can be used as filament.

Therefore, tungsten is used as the filament of an electric bulb.

Additional information:
In an incandescent bulb, the filament is the wire which is held by two wires. When an electric current is passed through the filament of the electric bulb, the filament gets heated and produces light.

Note:The students may think that if carbon was given in the options it may be the correct option. Because in the first electric bulb which was invented in 1869 by Joseph Swan, carbon filament was used. But because it does not satisfy all the given conditions, now tungsten is used as filament in the electric bulb.