Matric Part 1/9th Class Physics Chapter 9 Long Question With Answer for Unit 9 Transfer of Heat

Question # 1

What are applications and consequences of radiation.

Ans 1: Applications and consequences of radiation:
Absorption of heat: different objects absorb different amounts of heat radiations falling upon them reflecting the remaining part.
Dependence: the amount of heat absorb by a body depends upon the color and nature of its surface.
Example: a black and rough surface absorb more heat than a white or polished surface. Since good absorbers are also good radiators of heat. Thus, a black colored body gets hot quickly in summer by absorbing heat from its surrounding. It cools down quickly by giving out its heat to its surroundings. The bottom of cooking posts is made black to increase the absorption of heat from fire.
Ans 2: Reflection: like light rays, heat radiations also obey the laws of reflection.
Dependence: the amount of heat reflected from an object depends upon its color and nature of the surface.
Example: white surface more heat than colored or black surfaces . Similarly , polished surfaces are good reflectors than rough surfaces and reflection of heat radiations is greater from polished surfaces. We wear white or light color clothes in summer , which reflect most of the heat radiations reaching us during the hot day. We polish the interior of cooking and hot pots for reflecting backmost of the heat radiation within them.

Question # 2

Write the uses of conductors and non-conductors

Ans 1: Uses of conductor: good conductors are used when quick transfer of heat is required through a body. Thus, cooker , cooking plates, boiler , radiators and condensers of refrigerators etc. are made 0f metals such or aluminum as copper . Similarly, metal box are used for making ice creams, etc..
Ans 2: Uses of insulators: insulators or bad conductor are used in home utensils such as handles of sauce-pans, hot plate, spoons etc. They are made of wood or plastic. Air is one of the bad conductor or best insulator.
- Cavity walls separated by an air space and double glazed windows keep the houses warm in winter and cool in summer
- Materials which trap air i.e. wool, felt, fur, feathers, polystyrenes, and fiber glass are also bad conductors. Some of these materials are used for laggings to insulate water pipes, hot water cylinders, ovens, refrigerators,, walls and roofs of houses.
- Woolen cloth is used to make warm winter clothes.

Question # 3

What is conduction. Explain it briefly

Ans 1: Conduction: the mode of transfer of heat by vibrating atoms and free electrons in solids from hot to cold parts of a body is called conduction of heat.Example: the handle of metal spoon held in hot water soon gets warm. But in case of a wooden spoon, the handle does not get warm. Bot the materials behave differently regarding the transfer of heat. Metals are better conductors of heat than non-metals.
Ans 2: Conduction in solids: in solids, atoms and molecules are packed close together. They continue to vibrate about their mean position. The atoms or molecules present at the end begin to vibrate more rapidly. They also collide with their neighboring atoms or molecules. In doing so, they pass some of their energy to neighboring atoms or molecules during collisions with them with the increase in their vibrations. These atoms or molecules in turn pass on a part of the energy to their neighboring particles. In this way some heat reaches the other parts of the solids. This is a sow process and very small transfer of heat takes palace from hot to cold parts in solids.
Ans 3: Conduction in metals: metals have free electrons. These free electrons move with very high velocities within the metal objects. They carry energy at a very fast rate from hot to cold parts of the object as they move.Conclusion: thus heat reaches from hot parts of metals to cold parts much more quickly
Ans 4: Conduction in non-metals: non-metals are bad conductor of heat and the substances through which heat does not conduct are called bad conductors or insulators.Example: wood, cork, cotton, wool, glass, rubber, etc. are bad conductors or insulators.Conclusion: non-metals are insulators thus heat does not conduct through it.

Question # 4

Write the uses of conductors and non-conductors.

Ans 1: Uses of conductor: good conductors are used when quick transfer of heat is required through a body. Thus, cooker , cooking plates, boiler , radiators and condensers of refrigerators etc. are made 0f metals such or aluminum as copper . Similarly, metal box are used for making ice creams, etc..
Ans 2: Uses of insulators: insulators or bad conductor are used in home utensils such as handles of sauce-pans, hot plate, spoons etc. They are made of wood or plastic. Air is one of the bad conductor or best insulator.
- Cavity walls separated by an air space and double glazed windows keep the houses warm in winter and cool in summer
- Materials which trap air i.e. wool, felt, fur, feathers, polystyrenes, and fiber glass are also bad conductors. Some of these materials are used for laggings to insulate water pipes, hot water cylinders, ovens, refrigerators,, walls and roofs of houses.
- Woolen cloth is used to make warm winter clothes.

Question # 5

What is sea an land breezes? also explain the gliding and their uses

Ans 1: Sea breeze: on a hot day, the temperature of the land increases more quickly than the sea. It is because the specific heat of land is much smaller as compared to water. the air above land gets hot and rise up. Cold air from the sea begins to move towards the land as illustrated. It is called sea breeze.
Ans 2: Land breeze: at night, the land cools faster than the sea. Therefore, air above the sea is warmer, rises up and the cold air from the land begin to move toward s the sea as illustrated. It is called land breeze.

Question # 6

What is greenhouse ? also explain
t he greenhouse effect in global warming.

Ans 1: Greenhouse: a greenhouse is a heat trip. It is made of glass or transparent polythene sets that allow only radiations of short wavelength to pas through them. Radiation of long wavelength cannot enter or escape from green house.
Uses; greenhouse is usually used for plant growth
Ans 2: Phenomenon of maintenance of temperature in greenhouse : light from the sun contains thermal radiations ( infrared) of long wavelength as well as light and ultraviolet radiations of short wavelength to pas through easily but not long wavelength of thermal radiations. Thus, a green house becomes a heat trap.
radiations from the sun pass easily through glass and warms up the objects in a green house . These objects and plants give out radiations of much longer wavelengths. Glass and transparent polythene sheets don not allow them to escape out easily and are reflected back in the green house . This maintains the inside temperature of the green house . Greenhouse effect promise better growth of some plants.
Ans 3: Greenhouse effect: green house effect is rising of temperature because of trapping of heat energy by green house gases such as carbon dioxide , etc. in the temperature.
Ans 4: mechanism of green house effect: carbon dioxide in the atmosphere and water behave in a similar way to radiations as glass or polythene. Earths atmosphere contains carbon dioxide and water vapors. It causes greenhouse effect and thus maintains the temperate of the earth. During the recent years, the percentage of carbon dioxide has been increased considerably. This has caused an increase in the average temperature of the earth by trapping more heat due to greenhouse effect
Ans 5: Global warming: the average rise in the temperature of the earth by trapping more heat due to greenhouse effect is called global warming.
Effect of greenhouse in global warming: during the recent years, the percentage of carbon dioxide has been increased considerably by rapid use of fuels. This has caused an increase in the average temperature of the earth by trapping more heat due to greenhouse effect. This phenomenon is known as global warming. This has serious implications for the global climate.

Question # 7

Describe use of Leslie cube

Ans 1: Leslie's cube: a Leslie cube is a meta box having forces of different nature and it used to identify the emission of radiation.
Ans 2: Faces of Leslie's cube: the four faces of Leslie's cube may be as follow:
1. A shining silvered surface
2. A dull black surface
3. A white surface
4. a colored surface
Ans 3: Explanation: hot water is filled in the Leslie cube is placed with one of its face toward a radiation detectors. The rate a t which various surface absorb heat also depends upon the nature of those surface.
Ans 4: Example: take two surfaces, one is dull black and the other is a silvered polished surface, with a candle at the middle of the surface. It is found that
- A dull black surface is a good absorber f eat.
- A polished surface is a poor absorber of heat
Ans 5: Conclusion: the conclusion draw from the above is shown below
Surface: emitter, absorber, reflector
Dull black surface: best, best, worst
Colored surface: good, good, bad
White surface: bad, bad, good
Shining silver surface : worst, worst, best

Question # 8

What causes a glider to remain in air? describe

Ans 1: Gliding: a glider looks like a a small aeroplane without engine. Glider pilots use upward movement of hot air currents due to convection of heat. these rising currents of hot air are called thermals.
Gliders ride over these thermals. The upward movement of air currents in thermals hep them to stay in air for a long period.
Ans 2: Uses; the birds stretch out their wings and circle in these thermals. The upward movement of air helps birds to climb up with it. Eagles hawks and vultures are expert thermal climbers. after getting a free lift, birds are able to fly for hours without flapping their wings . They glide from one thermal to another and thus travel through large distances and hardly need to flap their wings.

Question # 9

what measures may b taken to save energy?

Ans 1: In houses good thermal insulator means lower consumption of fuel.
Ans 2: Measure to save energy: for this , following measures may be taken to save energy
- Hot water tanks are insulated by plastic or foam lagging
- Wall cavities are filled with plastic foam or wool
- Ceiling of rooms is covered by in insulating material( false ceiling)
- Double glazed window panes are used. These windows panes have air between sheets that provides good insulation.

Question # 10

What is convection and convection currents in air? also write its uses

Ans 1: Convection; transfer of heat by actual movement of molecules from hot place to a cold place is known as convection
Ans 2: Explanation: liquids and gases are poor conductors of heat. however, heat is transferred through fluid(liquid or gases) easily by another method called convection. A liquid or a gas becomes lighter as it expands on heating. Hot liquid or gas rises up above the heated area. The cooler liquid or gas from the surroundings gills the place which in turns is heated up. In this way, all the fluid is heated up. Therefore, transfer of heat through fluids takes place by the actual movement of heated molecules from hot to cold parts of the fluid.
Ans 3: Experiment: take a beaker r and fill two third of it with water. heat the beaker by keeping a burner below it. Drop two three crystals of potassium permanganate in the water. It will seen that colored streaks of water formed by the crystals move upwards above the flame and then move downward from side ways. These colored streaks show the path of currents in the liquid. when the water at the bottom of the beaker gets hot , it expands ,become lighter and rise up. While the cold but denser water moves downward to take its place.
Ans 4: Convection of currents: gases also expand on heating, thus convection currents are easily set up due to the difference in the densities of air at various parts in the atmosphere.
Ans 5: Uses of convection currents: convection currents set up by electric, gas or coal heaters help to warm our homes and offices central heating system in building work on the same principle by convection. Convection currents occur on a large scale in nature. The day-by-day temperature changes in the atmosphere result from the circulation of warm or cold air that travels across the region. land and sea breeze rea also the example of convection current.