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  4. Class IX
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  6. Class VII
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  8. Class V

Chapter 4: Heat

Question 1: State the similarities and differences between a clinical thermometer and a laboratory thermometer.Answer: Similarities between the laboratory thermometer and the clinical thermometer
  1. Laboratory thermometer and the clinical thermometer thermometers consist of long narrow uniform glass tubes.
  2. Laboratory thermometer and the clinical thermometer have a bulb at one end.
  3. Laboratory thermometer and the clinical thermometer contain mercury in the bulb.
  4. Laboratory thermometer and the clinical thermometer use Celsius scale on the glass tube.
Differences between the laboratory thermometer and the clinical thermometer:A clinical thermometer reads temperature 35°C to 45°C while the range of laboratory thermometer is -10°C to 110°C.The clinical thermometer has a kink near the bulb while there is no kink in the laboratory thermometer. Due to kink, mercury does not fall down on its own in clinical thermometer.Question2: Give two examples each of insulators and conductors of heat.Answer:
  • Conductors – silver, copper
  • Insulators – rubber, plastic.
Question3:Complete the sentence with appropriate answers:
  1. ____________ can determine an object’s hotness.
  2. ___________ Thermometer cannot be used to measure the temperature present in boiling water.
  3. __________ Degree is used to measure temperature.
  4. ___________ requires no medium for heat transfer for the process.
  5. An ice-cold steel fork is dipped into a mug of hot water. The transfer of heat to the other end is by the process of ___________.
  6. ____________ Color clothes absorb heat better than clothes of light colors.
Answers:
  1. Temperaturecan determine the object hotness.
  2. ClinicalThermometer cannot be used to measure the temperature of boiling water.
  3. CelsiusDegree is used to measure temperature.
  4. Radiation requires no medium for heat transfer for the process
  5. An ice-cold steel fork is dipped into a mug of hot water. Transfer of heat to the other end is by the process of 
  6. Dark Color clothes absorb heat better than clothes of light colors.
Question 4:Match the following:
1. Land breeze blows during(a) day
2. Sea breeze blows during(b) summer
3. Dark colored clothes are preferred during(c) night
4. Light colored clothes are preferred during (d) winter
Answers:
1. Land breeze blows during(c) night
2. Sea breeze blows during(a) day
3. Dark colored clothes are preferred during(d) winter
4. Light colored clothes are preferred during (b) summer 
Question5: Wearing more layers of clothes during winter keeps us warmer than wearing only one thick piece of clothing. Discuss why.Answer: More layers of clothing actually keep us warmer in winters as they have a lot of space between them. That space gets filled up with air. Air is a bad conductor; it does not allow the body heat to escape out.Question6: Mark the places in which the heat is being transferred by convection, conduction and by radiation.Answer: Question7: Explain why buildings in the places that have hotter climate are advised to paint the outer walls white.Answer: Since the white color reflects heat, it helps the house to not get heated up so much.Question8: When a liter of water at 50°C is mixed with another liter of water at 30°C what will be the temperature of the mixture?(1)80°C (2) lesser than 80°C but greater than 50°C(3) 20°C (4) Between 50°C and 30°CAnswer: (4)Between 50°C and 30°CQuestion9: In a mug that contains water at 40°C, an iron ball which is 40°C is dropped. Mention the flow of heat:
  1. Flow from the iron ball to water.
  2. Will not flow from water to iron ball or from iron ball to water.
  3. Will flow from the water to the iron ball.
  4. Both the temperatures increase.
 Answer: (2) Will not flow from water to iron ball or from iron ball to water.Question10: A wooden fork is dipped in a bowl of ice-cold water and its other end:
  1. Becomes cold due to the process of convection
  2. becomes cold due to the process of radiation
  3. becomes cold due to the process of conduction
  4. Doesn’t become cold.
Answer: (4) Doesn’t become cold.Question 11: Why stainless steel pans that we use at home is are provided with copper bottoms? The reason might be:
  1. Such type of pans appear to be colorful
  2. Copper is a much better conductor of heat than that of stainless steel.
  3. Copper is much easier to clean after use when compared to that stainless steel
  4. Copper bottoms in pans are more durable.
Answer:(2) Copper is a much better conductor of heat than that of stainless steel.