Pstti -Introduction of lightPresentation Transcript
A day is when there is light everywhere and the
We can see everything around us during day.
A day is from sunrise to sunset.
A night is when the sun does not shine and
everything is dark
We can see the moon and stars in the sky.
Night is from the sunset to sunrise.
It is necessary to have the electric lights on at
Day time activities
We work and play
Night time activities
We sleep and rest at night
Some people work at night
Some animals hunt at night
The cycle of day and night
The day and night system
helps us to live better on
When the sun comes up in
the morning we get up and
ready to go to school, work or
When it is night, we end up
our activities and go to sleep.
We use this cycle of day as the
way to identify when we
should be active and when
we should rest.
What causes day and night?
To answer the question let us do this
Take a globe and a torch.
Assume that the globe is the Earth and
torch is the Sun.
Now place the globe on the table and
throw the light of the torch on it.
Half of the globe will be lighted up.
The other half will be dark.
Day and night
Now slowly rotate the globe
The half that was dark will be lighted .
The half that was lighted will be dark.
This shows that only that half of the
globe that faces the torch gets light.
In the same way , when the Earth
rotates from west to east, only half of it
faces the sun.
This half which faces the sun has day .
The other half which does not get
sunlight has night.
When the earth rotates, day
changes to night and night
changes to day.
Thus the rotation of the
Earth causes day and night.
Earth makes one complete
rotation every 24 hours.
A whole day lasts 24 hours
and consists of
day(light) and night(dark).