Temperature and Its Measurement – Long Answer Type Questions
Class 6 Science — Chapter 7: Temperature and Its Measurement
Content Bank — Topics Covered
This set covers: temperature & heat, thermometers and scales, reading thermometers and precautions, changes of state (melting, freezing, evaporation, boiling, condensation, sublimation), heat transfer (conduction, convection, radiation), practical activities and real-life applications.
Long Answer Type Questions — Topic-wise (30 Questions)
Each answer is concise yet detailed, suitable for CBSE Class 6 examination answers.
Basics: Temperature & Heat (Q1–Q7)
1. What is temperature? Explain with an example how temperature indicates particle motion.
Temperature is a measure of how hot or cold a body or environment is and represents the average kinetic energy of the particles in a substance. When temperature increases, particles move faster; for example, when water is heated, its molecules vibrate and move more rapidly — eventually they may separate enough to become vapour. Conversely, when water is cooled, particle motion slows down and can lead to freezing. Temperature thus gives us a quantitative idea of particle motion inside matter.
2. Distinguish between heat and temperature with suitable examples.
Heat is energy that flows from a hotter object to a colder one due to a temperature difference, while temperature measures the degree of hotness or coldness of an object. For example, a large tub of lukewarm water may contain more heat energy than a small cup of hot coffee (because of greater mass), but the cup of coffee has a higher temperature. Heat depends on mass and specific heat capacity, whereas temperature is an intensive property independent of the amount of material.
3. Explain thermal equilibrium with a classroom example.
Thermal equilibrium occurs when two or more bodies in contact reach the same temperature and there is no net heat flow between them. For example, if a warm mug of tea is placed in a room, heat flows from the mug to the cooler air until both the mug and surrounding air reach the same temperature. At that point, the system is in thermal equilibrium and heat exchange stops.
4. Why does temperature affect the speed of chemical reactions? Give an example.
Temperature affects reaction rates because higher temperatures increase the kinetic energy of particles, causing them to collide more frequently and with greater energy — this increases the chance of successful reactions. For instance, dissolving sugar in hot tea happens faster than in cold tea because higher temperature helps sugar molecules disperse quicker and react with the solvent more rapidly. Many enzymatic reactions in biology are also temperature-dependent.
5. How is the concept of temperature useful in daily life? Give three examples.
Temperature measurement is useful in many daily situations: (1) Measuring body temperature with a clinical thermometer helps detect fever and illness; (2) Cooking — knowing boiling and baking temperatures ensures food is prepared safely; (3) Weather — temperature readings help us choose suitable clothing and plan outdoor activities. Accurate temperature control is also vital in refrigeration and heating systems to preserve food and maintain comfort.
6. Explain why metal feels colder than wood at the same room temperature.
Metal feels colder because it conducts heat away from the hand faster than wood. At the same temperature, both materials are at thermal equilibrium with the room, but metal has higher thermal conductivity so it draws heat from the warmer hand more quickly, causing the skin temperature to drop locally and producing a sensation of cold. Wood is a poorer conductor (insulator), so it transfers heat more slowly and feels warmer to touch.
7. Define the terms: conductor and insulator. Provide two examples of each in the context of heat.
A conductor is a material that allows heat (or electricity) to pass through it easily; examples for heat conductors include copper and aluminium (used in cookware). An insulator resists heat flow and helps prevent heat transfer; examples include wood and wool (used for handles and clothing to reduce heat loss).
Thermometers & Scales (Q8–Q14)
8. Describe the structure and working of a liquid-in-glass laboratory thermometer.
A liquid-in-glass laboratory thermometer consists of a narrow capillary tube attached to a bulb filled with a liquid such as mercury or coloured alcohol. When temperature rises, the liquid expands and moves up the capillary; when temperature falls, it contracts and moves down. The glass tube has a calibrated scale (usually in °C) which allows the user to read the temperature by noting the level of the liquid column against the marked scale. The wide bulb provides a reservoir for the liquid and increases sensitivity.
9. What is a clinical thermometer and how is it different from a laboratory thermometer?
A clinical thermometer is designed specifically to measure human body temperature. It typically has a curved or kinked capillary to retain the maximum reading and covers a small temperature range (around 35–42°C) for higher accuracy around body temperatures. A laboratory thermometer measures a wider temperature range for experiments and may not have the kink; it is less suited for precise body temperature readings due to its scale and range.
10. Explain the Celsius temperature scale and its fixed points. Why is Celsius commonly used in India?
The Celsius scale is based on two fixed points: the freezing point of pure water at standard atmospheric pressure (0°C) and the boiling point of water (100°C). The interval between these two fixed points is divided into 100 equal parts called degrees Celsius. Celsius is commonly used in India and most countries because it is simple, decimal-based, and practical for everyday measurements, education, and scientific work compared to the older Fahrenheit system.
11. How do you convert a temperature from °C to °F? Provide the formula and an example conversion (25°C to °F).
To convert Celsius to Fahrenheit use: T(°F) = T(°C) × 9/5 + 32. For 25°C: T(°F) = 25 × 9/5 + 32 = 25 × 1.8 + 32 = 45 + 32 = 77°F. So, 25°C equals 77°F.
12. What precautions should be taken while using and reading a glass thermometer?
When using a glass thermometer, hold it vertically at eye level to avoid parallax error; do not apply direct flame or heat to the thermometer; avoid striking or dropping it to prevent breakage; do not use a mercury thermometer for very high temperatures or where it may break dangerously; after use, clean it and store safely. If a mercury thermometer breaks, avoid direct contact with mercury and inform a teacher or responsible adult due to toxicity.
13. Describe how a digital or infrared thermometer measures temperature and one advantage over liquid-in-glass thermometers.
A digital thermometer uses an electronic sensor (thermistor or thermocouple) to measure temperature and displays the reading digitally. An infrared (non-contact) thermometer measures thermal radiation emitted by an object to estimate its surface temperature. One advantage is that digital/infrared thermometers are faster, safer (no risk of mercury spills), and often easier to read accurately without parallax errors.
14. The boiling point of water is lower in high mountains. Explain why with reference to pressure.
Boiling occurs when vapour pressure of a liquid equals atmospheric pressure. At high altitudes, atmospheric pressure is lower, so the vapour pressure required for boiling is reached at a lower temperature. As a result, water boils at temperatures below 100°C in mountains. For example, at higher elevations cooking processes may take longer because water boils at a lower temperature.
Changes of State (Q15–Q21)
15. Describe melting and freezing with examples. Define melting point and freezing point.
Melting is the change of a solid into a liquid on heating; for example, ice melts to water. Freezing is the reverse — the change of a liquid to a solid on cooling; water freezes to form ice. The melting point is the temperature at which a solid turns into a liquid, and the freezing point is the temperature at which a liquid turns into a solid. For pure water at 1 atmosphere, both are at 0°C (though supercooling and impurities can shift apparent values).
16. Explain evaporation and boiling. Mention two differences between them.
Evaporation is the slow change of a liquid into vapour from the surface at any temperature; boiling is rapid vaporisation that occurs throughout a liquid at a specific temperature (the boiling point). Differences: (1) Evaporation occurs at the surface and can happen at any temperature, while boiling occurs throughout the liquid at its boiling point. (2) Evaporation is usually slower and causes cooling of the remaining liquid (e.g., sweating cools the body), while boiling is fast and involves bubble formation within the liquid.
17. What is condensation? Give an example and explain where it is observed in daily life.
Condensation is the change of vapour into liquid when the vapour cools. An example is water droplets forming on the outside of a cold glass of water — warm water vapour in the air cools on contact with the cold surface and forms liquid droplets. Condensation is also observed as dew on grass in the morning and as water droplets on the bathroom mirror after a hot shower.
18. Define sublimation and give a real-life example. Why does sublimation occur for certain substances?
Sublimation is the process where a solid changes directly into gas without passing through the liquid state, such as dry ice (solid carbon dioxide) turning into carbon dioxide gas. Sublimation occurs for substances whose vapour pressure is sufficiently high at or near room temperature so that they transition directly to gas; it also depends on molecular structure and pressure conditions.
19. What is latent heat? Explain its role during melting and boiling.
Latent heat is the energy absorbed or released during a change of state without changing the temperature. During melting, latent heat (heat of fusion) is absorbed to break bonds in the solid and convert it to liquid; during boiling, latent heat (heat of vaporisation) is absorbed to change liquid to gas. Because of latent heat, temperature remains constant while state change occurs, even though energy is being added or removed.
20. How does adding salt to ice help melt it faster? Explain the principle involved.
Adding salt to ice lowers the freezing point of water (freezing point depression). Salt dissolves in the thin film of water on the ice surface, making it harder for water molecules to arrange into ice, so ice melts at a lower temperature. This principle is used in de-icing roads in winter where salt helps melt ice faster than pure water would under the same temperature conditions.
Heat Transfer: Conduction, Convection & Radiation (Q21–Q26)
21. Describe conduction with an experiment you can perform in class to demonstrate it.
Conduction is heat transfer through direct contact of particles, common in solids. A classroom experiment: Fix small beads of wax or pins along two rods, one metal and one wooden, and apply heat to one end of both rods (teacher-supervised). The beads on the metal rod will fall off sooner as heat travels faster through metal, demonstrating conduction. This shows metals are good conductors while wood is a poor conductor.
22. Explain convection with a simple diagrammatic description and an everyday example.
Convection is heat transfer by movement of fluid (liquid or gas) caused by differences in density when heated. Diagrammatically, heated fluid near a heat source becomes less dense and rises, while cooler denser fluid sinks, creating a circular current. Everyday example: Boiling water — warm water at the bottom rises while cooler water descends, forming convection currents that heat the pot evenly. Another example is warm air rising from a heater and cool air replacing it.
23. What is radiation? How does radiation from the Sun heat the Earth? Give one important safety note about radiation from very hot objects.
Radiation is heat transfer through electromagnetic waves and does not require any medium. The Sun emits electromagnetic radiation (including visible light and infrared) that travels through the vacuum of space and heats the Earth's surface when absorbed. Safety note: Radiation from very hot objects (like a fire or furnace) can cause burns without direct contact; maintain safe distance and use protective shields or clothing to prevent burns from intense radiant heat.
24. Compare conduction, convection and radiation in a tabular form with one example each.
Conduction: Transfer via direct contact; example — metal spoon in hot soup. Convection: Transfer via fluid movement; example — boiling water currents. Radiation: Transfer via electromagnetic waves; example — warmth from the Sun. (Key comparisons: conduction needs contact and works best in solids; convection requires fluid motion; radiation needs no medium.)
25. How does a thermos flask minimize heat transfer? Explain the design features used.
A thermos flask minimizes heat transfer using a vacuum between two walls to prevent conduction and convection; reflective coatings (silvering) on the inner surfaces reduce radiation; cork or plastic stoppers reduce heat loss/gain at the opening. Together these features keep hot liquids hot and cold liquids cold by greatly reducing all three modes of heat transfer.
Practical Applications & Experiments (Q26–Q30)
26. Design a simple class experiment to measure and compare evaporation rates under different conditions. Mention observations and conclusion.
Take three identical shallow dishes with equal amounts of water. Place one in sunlight, one in shade, and one near a fan. Measure and record water volume or mass at regular intervals (e.g., every hour). Observations: the dish in sunlight and the one near the fan will lose water faster than the one in shade, showing higher evaporation rates with increased temperature and air movement. Conclusion: Evaporation increases with temperature and airflow because particles gain energy and are removed from the surface more quickly.
27. Explain how a refrigerator works using the principles of temperature and heat transfer.
A refrigerator uses a circulating coolant (refrigerant) that absorbs heat from the interior as it evaporates at low pressure in the evaporator coil. The refrigerant gas is compressed (raising its temperature) and then passed through condenser coils outside the fridge where it releases heat to the surroundings and condenses back to liquid. The liquid refrigerant expands and evaporates again inside, absorbing more heat. This cycle removes heat from the fridge interior and expels it outside, keeping the inside cool.
28. Discuss how clothing helps maintain body temperature in different weather conditions.
Clothing helps maintain body temperature by providing insulation and controlling heat transfer. In cold weather, layered clothing traps air (a good insulator) close to the body, reducing heat loss by conduction and convection. Materials like wool are poor conductors and retain warmth. In hot weather, light and breathable fabrics allow sweat to evaporate, which cools the body through evaporation. Colour and fabric thickness also influence heat absorption and retention.
29. How does altitude affect cooking time and what adjustments should be made when cooking at high altitudes?
At high altitudes, lower atmospheric pressure causes water to boil at lower temperatures, so foods that are cooked by boiling may take longer to cook. To adjust, increase cooking time, use pressure cookers (which raise pressure and boiling point) or adjust recipes for longer simmering. Bakers may need to adjust baking times and temperatures due to lower boiling points of liquids in batter and changes in air density.
30. Summarize the key points a student should remember from Chapter 7 for a CBSE exam.
Key points: (1) Temperature measures how hot or cold an object is; heat is energy transfer due to temperature difference. (2) Thermometers (clinical and laboratory) are used to measure temperature; Celsius is the common scale with 0°C and 100°C as fixed points. (3) Changes of state — melting, freezing, evaporation, boiling, condensation, sublimation — are linked to temperature changes and involve latent heat. (4) Heat is transferred by conduction, convection and radiation. (5) Practical skills: reading thermometers correctly and following safety measures. Understanding these basics with practical examples and experiments is essential for CBSE Class 6 exams.
Note: These long answer questions and model answers are strictly aligned to the NCERT Class 6 Science syllabus for Chapter 7 and are intended for focused board exam practice.