Page 34 - ICSE Chemistry 8

• Glowing of an electric bulb on the passage of electric current: Electric current passes through the
fi lament of the bulb when an electric bulb is switched on. The fi lament glows to give light. The
bulb stops glowing when the light is switched off as the fi lament returns to its normal condi on.
No new substance is formed in this process. Hence glowing of an electric bulb is a physical change.

Mel ng of bu er, freezing of water, magne sing an iron bar by means of electricity, sublima on of
ammonium chloride and camphor, crystallisa on of sugar and bending a glass tube by hea ng are some
other example of physical change.
Thinking Fountain
Let’s perform some ac vi es to understand physical changes. Why is boiling of water a
physical change?

Activity 2.3

Aim: To understand that cu ng of paper is a physical change

Materials required: A sheet of paper, a pair of scissors
Procedure
• Take a sheet of paper and cut it into four square pieces.

• Take a square piece and further cut it into four square pieces.
• Now try to join all the square pieces by keeping them on a table.

Observa on: You will observe that all the square pieces cannot be joined back to acquire the original
shape of the paper. But each piece retains the property of paper.
Conclusion: Thus, cu ng of paper is a physical change.

Activity 2.4

Aim: To understand that mel ng of ice is a physical
change

Materials required: A glass tumbler, some ice after
cubes, an ice tray 10–15 minutes
Procedure
ice cubes water
• Take some ice cubes in a glass tumbler.

• Keep the tumbler at room temperature for
10–15 minutes.
Observa on: You will observe that the ice cubes
melt into water. after
30–40 minutes
Procedure
• Now take this water and pour it in an ice tray.
pouring water ice cubes
• Keep the ice tray in the freezer for 30–40 into an ice tray
minutes.

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