Temperature and Its Measurement – Case-based Questions with Answers

CBSE Class 6 Science - Chapter 7: Temperature and Its Measurement — 20 Case-Based Q&A

Content Bank — Focus Areas

Thermometers and reading techniques, temperature scales, effects of temperature on states of matter, heat transfer (conduction, convection, radiation), practical activities and real-life applications.

20 Case-Based Questions — NCERT Aligned

Read each short case carefully and answer the questions that follow. Model answers are provided for revision.

Case 1 — Fever Check

Riya feels hot and the teacher asks her to check her temperature using a clinical thermometer. The thermometer shows a reading of 38.2°C.

Q: What does this reading tell you? What precautions should be taken while using the clinical thermometer?

A: 38.2°C indicates that Riya has a fever (normal body temperature ≈ 36.5–37.5°C). Precautions: use the thermometer as instructed, hold it correctly, do not use a laboratory thermometer for body, clean it before and after use, and handle carefully to avoid breakage. Inform guardians and seek medical advice if needed.

Case 2 — Melting Ice

In a lab, students place an ice cube on a plate at room temperature and observe it melt gradually.

Q: Explain the process occurring and name the energy involved. Why does the temperature of ice-water mixture remain at 0°C while melting?

A: Melting is the change of state from solid to liquid due to heat absorption. The energy involved is heat (latent heat of fusion). During melting, energy is used to break the bonds between ice particles, not to raise temperature, so the temperature remains at 0°C until all ice melts.

Case 3 — Boiling at High Altitude

An experiment on a hill shows water boiling at 95°C.

Q: Why is the boiling point lower here than 100°C? How does this affect cooking?

A: At high altitudes atmospheric pressure is lower, so water boils at a lower temperature. This reduces the cooking efficiency of boiling; food may take longer to cook, so longer cooking times or pressure cookers may be needed.

Case 4 — Wet Clothes Dry Faster in Sun

Two identical clothes pieces are left to dry — one in sun, one in shade. The cloth in sun dries faster.

Q: Explain the reasons for different drying rates referring to evaporation.

A: Evaporation is faster in sunlight because higher temperature increases particle energy, enabling more molecules to escape into vapour. Sunlight also provides energy and may increase airflow, both accelerating evaporation compared to the shaded cloth.

Case 5 — Metal vs Wood Handle

Sara holds a metal spoon and a wooden spoon from the same hot pot. The metal spoon feels hotter at the end she holds.

Q: Explain why the metal handle feels hotter or colder compared to wood when in contact with heat.

A: Metal is a better conductor than wood, so it transfers heat quickly to the hand, making it feel hotter (or colder) faster. Wood is an insulator and transfers heat slowly, feeling less hot.

Case 6 — Thermometer Reading Error

A student reads a thermometer from an angle and gets different readings each time.

Q: Identify the error and suggest how to avoid it.

A: The error is parallax error from not reading at eye level. To avoid it, hold the thermometer vertically and read the top of the liquid column at eye level for an accurate reading.

Case 7 — Dry Ice Demonstration

A teacher shows dry ice turning into gas without melting.

Q: What is this process called? Why does dry ice behave this way?

A: This process is sublimation: a solid changing directly into gas. Dry ice (solid CO₂) has vapour pressure and molecular properties that allow it to change directly to gas under normal conditions without becoming a liquid.

Case 8 — Thermos Keeps Soup Hot

A thermos keeps soup hot for hours while a normal bowl cools quickly.

Q: Explain how a thermos reduces heat loss naming the modes of heat transfer it minimizes.

A: A thermos uses a vacuum between walls to prevent conduction and convection; reflective coatings reduce radiation; and tight stoppers reduce heat loss through openings. Thus it reduces conduction, convection and radiation, keeping soup hot longer.

Case 9 — Evaporation Cools the Body

After exercise, sweating cools the body.

Q: Explain how evaporation of sweat cools the body.

A: When sweat evaporates from the skin, liquid water molecules absorb heat (latent heat of vaporisation) from the skin to become vapour. This heat removal cools the skin, lowering body temperature.

Case 10 — Using Salt to Melt Ice

Salt is sprinkled on icy roads to clear them faster.

Q: How does salt help melt ice? Name the phenomenon involved.

A: Salt dissolves in the thin film of water on ice and lowers the freezing point (freezing point depression), causing ice to melt at lower temperatures. This helps clear ice more effectively.

Case 11 — Thermometer in Oven

A student uses a laboratory thermometer to measure oven temperature and the thermometer breaks.

Q: Why did it break and what thermometer should be used instead?

A: The glass thermometer may not be designed for very high temperatures or direct flame and can break. Use a high-temperature laboratory thermometer rated for ovens or a digital thermometer designed for cooking to avoid breakage.

Case 12 — Floating Ice

Ice cubes float in water while pebbles sink.

Q: Explain why ice floats but stones sink referring to density.

A: Ice is less dense than liquid water because of its crystalline structure that leaves more space between molecules; stones are denser than water, so they sink. Floating depends on whether an object's density is less than the fluid's density.

Case 13 — Cooking in Pressure Cooker

At high altitude, a cook uses a pressure cooker to speed up cooking.

Q: Why is a pressure cooker useful at high altitudes? Explain the role of pressure and boiling point.

A: A pressure cooker increases the pressure above the liquid, raising the boiling point of water so it can reach higher temperatures and cook food faster. This compensates for lower boiling points at high altitudes.

Case 14 — Wind Chill Effect

Two students stand outside at same temperature; one feels colder in windy weather.

Q: Explain why wind makes a person feel colder though thermometer temperature is same.

A: Wind increases convective heat loss from the body, removing the warm layer of air near the skin faster, causing a greater cooling effect (wind chill) even when thermometer readings are identical.

Case 15 — Metal Rod Heating

A metal rod is heated at one end and the heat travels to the other end.

Q: Name the process occurring and why metals are chosen for cooking utensils.

A: The process is conduction — heat transfer through direct contact. Metals are used for cooking utensils because they are good conductors of heat and distribute heat efficiently for cooking.

Case 16 — Dew on Grass

In the early morning, water droplets are seen on grass even though it didn’t rain.

Q: Explain how dew forms with reference to condensation and temperature change.

A: Dew forms when warm moist air cools overnight and its water vapour condenses on cooler surfaces like grass. The temperature of the grass falls below the dew point causing condensation of vapour to liquid droplets.

Case 17 — Measuring Room Temperature

A student measures room temperature at different times and finds small fluctuations.

Q: What factors could cause these small changes and how to ensure consistent readings?

A: Factors include sunlight through windows, nearby heat sources, opening doors, and HVAC systems. To ensure consistency, place the thermometer away from direct sunlight and heat sources, keep it at a stable height, and take readings at the same location and time.

Case 18 — Insulation in Houses

Two houses, one insulated and one without insulation, have different indoor temperatures during winter.

Q: Explain how insulation works and name materials used for insulation.

A: Insulation reduces heat loss by trapping air and reducing conduction and convection. Materials like fiberglass, foam, wool and double-glazed glass are used to insulate homes, keeping them warmer in winter and cooler in summer.

Case 19 — Quick Chill

A customer wants to chill a drink quickly and adds ice and salt.

Q: Explain why adding salt to ice-water helps chill the drink faster.

A: Salt lowers the freezing point of water causing ice to melt and absorb more heat (latent heat) from the drink and surroundings. The extra melting/heat absorption cools the drink faster than ice alone.

Case 20 — Classroom Experiment Results

A class performed an experiment to compare evaporation in warm and cool rooms and recorded higher rates in the warm room.

Q: Provide a brief explanation using particle theory and suggest one control to make the experiment fair.

A: In a warm room particles of water have higher average kinetic energy, so more molecules escape from the liquid to vapour, increasing evaporation rate. A control suggestion: use identical containers with the same water volume and surface area to ensure differences are due to temperature alone.

Note: These case-based questions and answers are prepared strictly as per NCERT Class 6 Science Chapter 7 and are ideal for CBSE exam practice and application-based understanding.