Available Answers

1. 1.

   Fill in the blanks:

   1. Heat is the energy transferred between two bodies in contact due to the difference in their ____________.
   2. Wood, petrol, kerosene oil and LPG are ____________ substances.
   3. Do not wear any ____________ clothes while handling fire.
   4. The ____________of the thermometer should be made of thick glass to protect the capillary tube against any physical damage.
   5. The Kelvin scale has its ____________ set to absolute zero which is the  ____________ possible temperature that exists in the universe.
2. 2.

   State whether the following statements are true (T) or false (F). Correct the false statements:

   1. Conduction of heat takes place within a body and between the bodies in contact with each other.
   2. Mud houses are cooler in summer because mud is a bad conductor of heat.
   3. In thermometers, mercury expands due to conduction of heat.
   4. The rate of conductivity is same for all metals.
   5.  In liquids, heat is transferred due to vibration of the molecules.
   6. Air is a good conductor of heat.
3. 3.

   Fill in the blanks:

   1. Convection is the main mode of transfer of heat in ____________.
   2. ____________ are responsible for causing wind and monsoon rain.
   3. It is recommended that air conditioners and ventilators should be fixed near the ____________ of a room.
   4. All objects radiate heat but the amount of heat radiated from an object depends on its  ____________.
   5. Out of the two objects of the same material and mass, the one with ____________ surface area will absorb more radiation.
4. 4.

   Fill in the blanks:

   1. When heat is supplied to matter, the ____________ of its molecules increases and they are vibrating vigorously.
   2. Hard solids have ____________ point while soft solids have ____________ melting point.
   3. No medium is required to transfer heat by the process of ____________.
   4. A cold spoon dipped in a cup of hot milk transfers heat to its other end by the process is ____________.
   5. ____________ clothes absorb more heat than ____________ clothes.
   6. In ____________ heat is transmitted mainly by convection.
   7. Handles of frying pans are made of ____________ conductors of heat.
   8. Transfer of heat by ____________ is faster than conduction.
   9. During the night ____________ blows from land to sea.
   10. The sun emits more ____________ than an electric lamp because the ____________ the sun is very high.
   11. The heat which comes out of the hot object is called ____________ heat.
   12. Cooling coils in refrigerators are made of ____________ to conduct heat away.
5. 5.

   State whether the following statements are true (T) or false (F). Correct the false statements:

   1. The extent of expansion is different in different solids.
   2. Railway tracks expand in winters and contract in summers.
   3. Liquids and gases are poor conductors of heat.
   4. Non-metals have free electrons that help in transfer of heat.
   5. When fluids are heated, the molecules closer to the source get heated and expand.
   6. Hot air being less dense rises up.
   7. Shiny surfaces are bad radiators of heat.
   8. The higher the temperature of the surface, the greater is the amount of radiation emitted.
6. 6.

   Choose the correct option:

   1. An iron ball at 50 °C is dropped in a mug containing water at 50 °C. The heat will:

   1. flow from the ball to the water.
   2. flow from the water to the ball.
   3. will not flow.
   4. increase the temperature of both.

   2. What is the temperature of boiling water?

   1. 212 ºF
   2. 273 K
   3. 99 ºC
   4. 120 ºF

   3. Conduction is the mode of heat transfer in:

   1. solids
   2. liquids
   3. gases
   4. all of these
       

   4. Convection cannot take place in solids because:

   1. actual movement of particles is not possible
   2. solids possess free electrons
   3. atoms are loosely packed
   4. they are bad conductors

   5. Which of the following is an example of radiation?

   1. Heat from an electric bulb
   2. Heat from a bonfire
   3. Heat from red hot iron rod
   4. All of these

   6. The sides of the double walls of a thermos flask facing each other are made shiny because:

   1. shiny surfaces absorb more heat
   2. shiny surfaces are bad radiators of heat
   3. shiny surfaces are bad conductors
   4. none of these