Question

ill in the blanks:
Pure tungsten has _____________.
(A) Low resistivity and a high melting point
(B) High resistivity and a high melting point
(C) High resistivity and a low melting point
(D) Low resistivity and a low melting point

Answer 1

Hint Tungsten is used in electric bulbs. Light is radiated from it as the electric current flows through it. This energy is radiated as a drop in the electrical energy $E \propto {R^2}$ via resistance. As the energy is radiated in the form of heat and E – M waves we don’t want the bulb filament to melt down.

Complete step by step answer
Pure tungsten is used in bulbs.
Light is radiated from the bulb-filaments as a drop in electrical energy of the circuit. Now as the filament heats up a lot, it shouldn’t melt. It is a fact that we use tungsten for a filament.
Tungsten has a high melting point and high resistivity. Hence, option (b.) is the correct answer.

Additional information Tungsten is one of the transition metals, and is located in group six of the periodic table of chemical elements. It got its name from the mineral Wolframite, from which this is obtained. It looks like a shiny metal. The density of tungsten is very close to the density of gold that is why tungsten was used for faking gold bars. It is very hard; also, it has the highest tensile strength. However, these are not the main features of the metal.
To melt a piece of tungsten, we need to reach an extremely high temperature of 3422 degrees Celsius. That is why this metal was used as the filament of incandescent bulbs. However, if we pass a current through the tungsten filament, it can overheat and then break, thereby ceasing any production of light. Due to this fact, air tungsten oxidizes at a high temperature, forming on its surface oxides of tungsten. Also, a tungsten rod after calcination with a gas burner obtains beautiful colored stains, caused by the different thickness of the oxide film on the metal surface.
However, into light bulbs it’s not really about the beauty, more about the ability to actually produce light. Hence, all the oxygen from the bulb is pumped out and is replaced with a mixture of nitrogen and argon under reduced pressure. In this condition, the filament can shine for quite a long time.

Note
Look at the options and that would help us to eliminate the wrong ones. Clearly, we can’t use a low resistivity material because that way it wouldn’t heat up as much. Also, if the melting point is low then it’d break. So, the only option that suffices these conditions is option B