For Class VII Students, NCERT

1. Heat
Part-4
FOR CLASS VII
By- Vivek Singh
ABPS JAGDISHPUR

2. Key points in this power point
• Radiation
• Kinds of cloth we wear in summer and winter
• Wind
• Two types of winds
• Assignment

3. RADIATION
• Radiation is the process by which heat is transferred
from one place to another without the help of any
medium.
• E.g. :- The heat from the sun reaches the earth by
radiation. When we sit near a fire we feel warm due
to the heat radiated by the fire. All hot bodies
radiate heat.

4. Heat From the Sun
• You can feel the sun warm your skin on a sunny
day.
• This is because the energy causes the particles
in your skin to move faster = more heat energy.

5. Dark coloured surfaces and coloured
surfaces
• Dark coloured surfaces absorb more heat than
light coloured surfaces.
• Take two tin cans of the same size.
• Paint the outer surface of one black and the
other white.
• Pour equal amounts of water in each and leave
them in sunlight for about one hour.

6. • Measure the temperature of water in both the
cans.
• The water in the black can is warmer than the
water in the white can.

7. Dark coloured surfaces radiate more heat
than light coloured surfaces
• Take two tin cans of the same size.
• Paint the outer surface of one black and the
other white.
• Pour equal amounts of hot water of the same
temperature (say 80°C).

8. Containers with black and
white surface
• Leave them in a room or
shade for 10 to 15 minutes.
• Measure the temperature of
water in both the cans. The
water in the black can is
cooler than the water in the
white can.

9. Kinds of cloth we wear in summer and winter
• Dark coloured surfaces absorb more heat than
light coloured surfaces.
• Dark coloured surfaces radiate more heat than
light coloured surfaces.
• We wear dark coloured clothes in winter because
it absorbs more heat and keep us warm.

10. • We wear light coloured clothes in summer
because it reflects most of the heat and keeps
us cool.
• We wear woolen clothes in winter because wool is
a poor conductor of heat and the air in between
the wool fibers prevents loss of heat from our
body. So we feel warm.

11. Wind
• Wind is the horizontal movement of air from an
area of high pressure to lower pressure.
• There is uneven heating of earth that result in
Global Wind Pattern.

12. Two types of winds
Local Winds
Local winds are the winds that blow over short
distances.
Global Winds
Global winds are the winds that blow steadily
from specific directions over long distances.

13. Light and heavy air

14. Wind is caused by:
1) Differences in temperature.
2) Differences in pressure.

15. Differences in temperature
1. Warm air rises.
–Warming air make the molecules move faster
and spread out.
–This makes the air less dense.
–Less dense air is light and will rise.

16. 2. Cold air sinks.
–Cooling air makes the molecules move slower and
group together.
–This makes the air more dense.
–More dense air will sink.

17. Differences in pressure
1. Rising air creates Low pressure.
–If air is lifted up, that means there is Less air
pushing down on Earth.
2. Sinking air creates High pressure.
–If air is sinking, then air is pushing down on the
surface of Earth with a High amount of pressure.

18. Assignment
• Make note of all slides in your notebook.
• Write the summary of the chapter in your
notebook.
• Write how conduction and radiation are
different from each other.
• What is difference between local and global
wind?

19. THANK YOU