Page 95 - SCERT Kerala State Syllabus 8th Standard Basic Science Textbooks English Medium Part 1_Neat

All metals are conductors of electricity.

The ability of a substance to let
electricity pass through it is
known as electrical conductivity.
Silver is the best electrical
conductor among metals. Copper
and aluminium are also good
conductors of electricity. Still, the
electrical wires in our houses are
made of copper. Similarly, the
electric wires that we see on
electric posts outside our houses
Fig. 7.4 are made of aluminium. What
could be the reason?

$
$

$
Tap gently with a spoon on a metallic vessel and an earthen pot.
• What difference do you find?

• Is it advisable to use plastic or wood to make instruments
Fig. 7.5 like cymbals and bells?
• What kind of materials are used to make them? What could
be the reason for this?

The ability of metals to produce sound when tapped with a hard
material is known as sonority.-

Metals generally melt at high temperatures and possess high
Fig. 7.6 density.
However, metals like gallium, cesium and mercury melt at low
temperatures.

Metals like lithium, sodium and potassium are low density
metals.

94 Basic Science VIII