Page 218 - NCERT Science Class 10 English Medium

is highly damaging to organisms, for example, it is known to cause skin
cancer in human beings.
Ozone at the higher levels of the atmosphere is a product of UV
radiation acting on oxygen (O ) molecule. The higher energy UV
2
radiations split apart some moleculer oxygen (O ) into free oxygen (O)
2
atoms. These atoms then combine with the molecular oxygen to form
ozone as shown—
UV
→
O  O+O
2
O O → O
+
2 3
( Ozone)
The amount of ozone in the atmosphere began to drop sharply in
the 1980s. This decrease has been linked to synthetic chemicals like
chlorofluorocarbons (CFCs) which are used as refrigerants and in fire
extinguishers. In 1987, the United Nations Environment Programme
(UNEP) succeeded in forging an agreement to freeze CFC production at
1986 levels. It is now mandatory for all the manufacturing companies
to make CFC-free refrigerators throughout the world.

Activity
Activity 13.4
Activity 13.4
Activity 13.413.4
Activity 13.4
n Find out from the library, internet or newspaper reports, which
chemicals are responsible for the depletion of the ozone layer.
n Find out if the regulations put in place to control the emission of
these chemicals have succeeded in reducing the damage to the
ozone layer. Has the size of the hole in the ozone layer changed in
recent years?

13.2.2 Managing the Garbage we Produce

In our daily activities, we generate a lot of material that are thrown
away. What are some of these waste materials? What happens after we
throw them away? Let us perform an activity to find answers to these
questions.

13.5
Activity 13.5
Activity
Activity 13.513.5
Activity
Activity 13.5
n Collect waste material from your homes. This could include all
the waste generated during a day, like kitchen waste (spoilt food,
vegetable peels, used tea leaves, milk packets and empty cartons),
waste paper, empty medicine bottles/strips/bubble packs, old and
torn clothes and broken footwear.
n Bury this material in a pit in the school garden or if there is no
space available, you can collect the material in an old bucket/
flower pot and cover with at least 15 cm of soil.
n Keep this material moist and observe at 15-day intervals.
n What are the materials that remain unchanged over long periods
of time?
n What are the materials which change their form and structure
over time?
n Of these materials that are changed, which ones change the fastest?

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