Page 94 - SCERT Kerala State Syllabus 8th Standard Basic Science Textbooks English Medium Part 1_Neat

The filaments of electric bulbs are made of fine wires of tungsten
(Figure 7.2). Tungsten can be drawn into fine wires. Hence it is
used to make the filament.
Platinum is the most ductile metal. You may have seen metals
like copper, gold etc., being used as thin fine wires. This is due
to their high ductility.

Hardness is yet another property of metals.

However, there are quite a few metals which are soft. Let's do
an experiment. Take a small piece of sodium with a forceps Fig. 7.2
and try to cut it with a blade. Are you able to cut sodium? Can
you cut metals like copper, aluminium and iron like this? Just
try. Gallium and cesium are also soft metals.

Lithium, sodium and potassium are soft metals. We can easily
cut them with a knife.
Observe the newly formed surface of sodium when it is cut with
a knife. What peculiarity do you observe? Don't you see
something similar at the freshly cut surfaces of iron and copper
as well?

The surface newly formed when metals are cut, has a shining
appearance. This property is known as metallic lustre.

Is metallic lustre identical for all metals? Observe and find out.
• Metallic vessels are commonly used for cooking. Which
metals are commonly used to make utensils?

• Which characteristics of metals are made use of in this case?

The ability to conduct heat is an important property of metals.
This property is known as thermal conductivity.

Metals are thermal conductors.
Fig. 7.3
Silver is the best thermal conductor among metals. Aluminium,
copper etc., also possess comparatively high thermal
conductivity.

Basic Science VIII 93