Unit 10
HEAT
ON THE MOVE
Short
Questions:
Q1. What is
thermometer?
It is an instrument
used to measure the temperature.
Q2. Define conduction?
Heat always travel from
something hot to something cold, or from a hot part of something to a cold
part. This type of flow of heat is called conduction.
Q3. What are conductors?
Conductors:
The materials from
which heat and electricity can pass easily. e.g., Copper, Silver, etc.
Q4. What are insulators?
Insulators:
The materials from
which heat and electricity cannot pass.
e.g., wood, cork etc.
Q5. Define convection?
If air is heated, it
expands and rises. Cooler, heavier air moves in to take its place. This type of
flow of heat is called convection.
Q6. What is convection
current on wave?
The movement of warm
and cold gas or liquid produces a convection current or wave.
Q7. How heat transferred
in liquids and gases?
By convection, the heat
transferred in liquids and gases.
Q8. Define radiation
and radiant heat?
The flow of heat
without any medium is called radiation. The Sun’s heat energy that travels
through empty space is called radiant heat or infrared radiation.
Q9. What is land
breeze?
Land breeze:
At night, the land
cools down more quickly than the sea. The air over the sea is warmer and so it
rises. This produces land breeze.
Q10. What is sea breeze?
Sea breeze:
During the day, Sun
warms up the land more quickly than the sea. The warm air above the land rises.
The cold air from over the sea moves in to take its place so that during the
day cool breeze blow in from the sea.
Q11 What is global
warming?
The extra warming by
polluting gases and burning fossil fuels, in factories and vehicles etc. is
called global warming.
12. What is Green House
effect?
It is the natural
process that warms the earth’s surface. The absorbed energy of Sun warms the
atmosphere and the surface of Earth. It is called Green House effect.
Long
Questions:
Q1. Write a note on
conduction?
Conduction:
Heat always travel from
something hot to something cold, or from a hot part of something to a cold
part. This type of flow of heat is called conduction.
Everything is made up
of particles (atoms and molecules) that are moving. When heat flows into
something it makes these particles move faster. When heat is lost, they slow
down.
Example:
e.g., if we put a metal
spoon in a very hot drink, the handle of the spoon gets hot very quickly.
Good conductors of
heat:
Metals e.g., copper,
aluminium, silver etc. are best conductors of heat. This is because their
particles are packed closely together and so the vibrations are passed very
quickly.
Q2. Write detailed note
on the vacuum flask?
The vacuum
flask:
The vacuum flask keeps
hot drinks hot and cold drinks cold by stopping the movement of heat.
Construction:
The flask consists of a
glass bottle with double walls. There is a vacuum between these glass walls
which stops the conduction and convection of heat. Radiation of heat is
prevented because the walls of the glass have a Silver coating. The stopper is
made of a good insulating material such as cork, or hollow plastic.
Q3: How convection
current occurs in liquids?
Convection current in
Liquids:
Convection currents
also occur in water and other liquids.
The water in a pan over
a fire, gas ring, or hotplate is heated all through, even though the heat is
only applied at the bottom. This is because water circulates in the pan because
of convection.
The water near to the
base of the pan become warmer and expands. This water is less dense (lighter)
and so it rises.
Cooler water sinks to
take its place. This water movement continues until all the water is at the
same temperature.
