Exercises
1. Similarities and Differences between the Laboratory Thermometer and the Clinical Thermometer
Similarities:
- Both are used to measure temperature.
- Both have mercury inside to indicate the temperature.
- Both have a uniform glass tube with a scale.
Differences:
- The clinical thermometer has a kink to prevent the mercury level from falling, while the laboratory thermometer does not.
- Clinical thermometers measure temperatures between 35°C and 42°C, whereas laboratory thermometers have a wider range (usually -10°C to 110°C).
- Clinical thermometers are used for human body temperature, while laboratory thermometers are used for other objects.
2. Two Examples of Conductors and Insulators
Conductors:
- Copper
- Aluminum
Insulators:
- Plastic
- Wood
3. Fill in the Blanks
(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.
(d) No medium is required for the 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.
4. Match the Following
(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
5. Why Wearing More Layers of Clothing Keeps Us Warmer in Winter
Wearing multiple layers traps air between the layers, which acts as an insulator and reduces heat loss from the body. This keeps us warmer than wearing one thick piece of clothing.
6. Marking Heat Transfer in Fig. 3.13
- Conduction: Heat transfer from the flame to the metal rod or the pot.
- Convection: Heat transfer in the liquid as hot liquid rises and cooler liquid sinks.
- Radiation: Heat transfer from the flame directly to the surroundings.
7. Why Outer Walls of Houses in Hot Climates are Painted White
White surfaces reflect most of the sunlight, reducing heat absorption. This helps keep the interiors cooler in hot climates.
8. Temperature of the Mixture
The temperature of one liter of water at 30°C mixed with one liter at 50°C will be (d) between 30°C and 50°C.
9. Heat Transfer Between Iron Ball and Water
When an iron ball at 40°C is dropped in water at 40°C:
Answer: (b) Heat will not flow from the iron ball to water or from water to the iron ball because both are at the same temperature.
10. Wooden Spoon in Ice Cream
A wooden spoon dipped in ice cream:
Answer: (d) Does not become cold.
Explanation: Wood is an insulator and does not conduct heat effectively.
11. Stainless Steel Pans with Copper Bottoms
Stainless steel pans are provided with copper bottoms because:
Answer: (c) Copper is a better conductor of heat than stainless steel.
Extended Learning — Activities and Projects
1. Doctor Observation Questions: (a) To disinfect the thermometer.
(b) To measure the temperature closest to the core body temperature.
(c) Yes, the temperature can be measured at the armpit or rectum, but readings vary.
(d) Different parts of the body may show slight temperature variations.
2. Veterinary Doctor Inquiry:
Normal temperature of domestic animals:
- Cow: 38.5°C
- Dog: 38.3°C
- Bird: Around 40-42°C
3. Burning Paper Strip on Iron Rod:
The paper does not burn because the iron rod conducts heat away quickly, preventing the paper from reaching its ignition temperature.
4. Spiral Paper Activity:
The spiral rotates due to the heat from the candle causing air to rise (convection), which moves the paper.
5. Hot and Cold Water Bottle Experiment:
When the postcard is pulled, the hot water rises and mixes with the cold water due to convection currents. This happens because hot water is less dense and rises.
1. What material are woollen clothes made from?
Answer: Woollen clothes are made from animal fibres.
2. What material are cotton clothes made from?
Answer: Cotton clothes are made from plant fibres.
3. Why do we wear woollen clothes in winter?
Answer: Woollen clothes keep us warm by trapping air, which prevents heat from escaping our body.
4. Why do we prefer wearing light-colored clothes in summer?
Answer: Light-colored clothes reflect heat, helping us feel cooler in the summer.
5. How do we know whether an object is hot or cold?
Answer: We generally use our sense of touch to determine if an object is hot or cold, though it may not always be reliable.
6. What is the device used to measure the temperature of an object?
Answer: A thermometer is used to measure the temperature of an object.
7. What kind of thermometer is used to measure body temperature?
Answer: A clinical thermometer is used to measure body temperature.
8. What is the normal body temperature of a human?
Answer: The normal body temperature of a human is around 37°C.
9. Why can’t a clinical thermometer be used to measure the temperature of objects like hot milk?
Answer: A clinical thermometer is designed only to measure body temperature and should not be used for other objects. It could break if exposed to high temperatures.
10. What is the temperature range of a clinical thermometer?
Answer: A clinical thermometer measures temperatures between 35°C and 42°C.
11. What is the function of the kink in a clinical thermometer?
Answer: The kink prevents the mercury from falling back after the thermometer is removed from the body, ensuring an accurate reading.
12. What is the temperature range of a laboratory thermometer?
Answer: The temperature range of a laboratory thermometer is from –10°C to 110°C.
13. Why should a laboratory thermometer not be used to measure body temperature?
Answer: A laboratory thermometer has a wider temperature range and is not designed to measure the human body temperature accurately.
14. What is conduction?
Answer: Conduction is the transfer of heat from the hotter end to the colder end of an object, especially in solids.
15. What is the difference between conductors and insulators?
Answer: Conductors, like metals, allow heat to pass through them easily, while insulators, like wood and plastic, do not.
16. What materials are used to make pans with handles that don’t get hot?
Answer: Pans are made with handles from materials like plastic or wood, which are insulators and do not conduct heat easily.
17. What is convection?
Answer: Convection is the process of heat transfer in liquids and gases, where hot fluid rises and cold fluid sinks, creating a continuous circulation.
18. What causes the sea breeze?
Answer: During the day, the land heats up faster than the sea, causing the air over the land to rise, and the cooler air from the sea moves in, creating a sea breeze.
19. What causes the land breeze?
Answer: At night, the land cools faster than the sea, and the cooler air from the land moves towards the sea, creating a land breeze.
20. How does heat from the sun reach the Earth?
Answer: Heat from the sun reaches the Earth through radiation, which does not require any medium.
21. Why is it more comfortable to wear light-colored clothes in summer?
Answer: Light-colored clothes reflect most of the heat, helping to keep us cooler in summer.
22. Why do dark-colored clothes keep us warm in winter?
Answer: Dark-colored clothes absorb more heat, keeping us warmer in winter.
23. What is the function of woollen clothes in winter?
Answer: Woollen clothes trap air between the fibres, which prevents heat from escaping and keeps us warm.
24. What happens to the temperature of water in black and white cans placed in the sun?
Answer: The water in the black can heats up more quickly than the water in the white can because black surfaces absorb more heat.
25. What is the effect of using a thick blanket vs two thin blankets?
Answer: Two thin blankets are better than one thick blanket because the air trapped between the layers acts as an insulator, keeping you warmer.
26. What is the normal range of a clinical thermometer’s mercury level?
Answer: The mercury level should fall below 35°C before use.
27. What happens to the mercury level when a thermometer is taken out of hot water?
Answer: The mercury level starts to fall as the thermometer cools down.
28. Why must you wash a clinical thermometer before and after use?
Answer: To prevent contamination and ensure it is safe and hygienic to use.
29. What is radiation in heat transfer?
Answer: Radiation is the transfer of heat in the form of electromagnetic waves. It does not require a medium and can occur in a vacuum.
30. What are the precautions to be taken while using a clinical thermometer?
Answer: The thermometer should be washed before and after use, shaken to ensure the mercury is below 35°C, and handled carefully to avoid breaking.
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