Section outline

    • Q1. State similarities and differences between the laboratory thermometer and the clinical thermometer.

      Ans:

      Similarities of both the thermometers:

      1. They are used to measure temperature.
      2. They use celsius scale (°C).
      3. They have a long, narrow glass tube.
      4. They have a bulb containing mercury at one end.

      Differences:

      Clinical thermometer Laboratory thermometer
      It's temperature range is 35°C to 42°C. It's temperature range is  –10°C to 110°C.
      It has a kink near the bulb. Kink is absent.
      It measures temperature of human body. It measures temperature in the laboratory.
      Q2. Give two examples each of conductors and insulators of heat.

      Ans:

      Conductors are copper & aluminum.

      Insulators are plastic & wood.

      Q3. Fill in the blanks:

      Ans:

      (a) The hotness of an object is determined by its temperature.

      (b) Temperature of boiling water cannot be measured by a clinical thermometer.

      (c) Temperature is measured in degree Celsius (°C).

      (d) No medium is required for transfer of heat by the process of  radiation.

      (e) A cold steel spoon is dipped in a cup of hot milk. Heat is transferred to its other end by the process of conduction.

      (f) Clothes of dark colours absorb more heat better than clothes of light colours. 

      Q4. Match the following:

      Ans:

      (i) Land breeze blows during (d) night
      (ii) Sea breeze blows during (c) day
      (iii) Dark coloured clothes are preferred during (b) winter
      (iv) Light coloured clothes are preferred during (a) summer
      Q5. Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing .

      Ans:

      1. Wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece because each layer creates space which traps air.
      2. As air is a poor conductor of heat, it acts as an insulator preventing heat from our bodies to escape to the cold surroundings.
      Q6. Look at Fig. 3.13. Mark where the heat is being transferred by conduction, by convection and by radiation.

      Ans:

      Q7. In places of hot climate it is advised that the outer walls of houses be painted white. Explain.

      Ans:

      In places of hot climate, it is advised that the outer walls of houses be painted white because

      1. White colour reflects most of the heat that is incident on the walls,
      2. It is also poor absorber of heat.
      3. This helps keep the interior of the house cooler by preventing excessive heat absorption from the sun.
      Q8. One litre of water at 30°C is mixed with one litre of water at 50°C. The temperature of the mixture will be:

      Ans: 

      (d) between 30°C and 50°C

      (Because the hot water will lose heat and cold water will gain heat & this will keep the temperature between 30°C & 50°C)

      Q9. An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will:

      Ans:

      (b) not flow from iron ball to water or from water to iron ball.

      (because both are at the same temperature, so heat will not flow.)

      Q10. A wooden spoon is dipped in a cup of ice cream. Its other end:

      Ans:

      (d) does not become cold.

      (because wood is a bad conductor of heat.)

      Q11.  Stainless steel pans are usually provided with copper bottoms. The reason for this could be that:

      Ans:

      (c) copper is a better conductor of heat than the stainless steel.