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Chapter 7. Temperature and its Measurement

Chapter 7. Temperature and its Measurement

Temperature is an important concept in science that helps us understand how hot or cold an object is. Every day, we experience different temperatures around us, such as the warmth of sunlight, the coolness of water from an earthen pot, or the heat of boiling water. However, our sense of touch cannot always judge temperature correctly. Therefore, scientists use thermometers to measure temperature accurately. This chapter explains the concept of temperature, different types of thermometers, temperature scales, methods of measuring temperature, and their applications in daily life.

CBSE Full Notes

These detailed CBSE Notes are prepared according to the latest NCERT Curiosity textbook and the current CBSE competency-based pattern. The notes explain every important concept in simple language with suitable examples, tables, and revision points for effective learning and examination preparation.

Introduction to Temperature

Whenever we touch an object, we often describe it as hot, warm, or cold. For example, a cup of hot tea feels warmer than tap water, while ice feels much colder. Although these observations are useful in daily life, they are not always accurate. Our skin only gives us a sensation of heat or cold; it does not measure the exact temperature.

Scientists use the term temperature to describe the degree of hotness or coldness of an object. Temperature provides a numerical value, making comparisons more accurate and reliable than our sense of touch.

Why Our Sense of Touch is Not Reliable

Our skin adapts to the temperature of the object we touch. If one hand is placed in warm water and the other in cold water for a few minutes, both hands experience the same lukewarm water differently. The hand taken out of warm water feels the lukewarm water cold, while the hand taken out of cold water feels it warm.

This simple activity shows that our sense of touch depends on previous exposure and cannot accurately determine temperature. Therefore, scientific instruments are needed for correct measurements.

What is Temperature?

Temperature is the measure of the degree of hotness or coldness of a body. It indicates how hot or cold an object is compared to another object.

Temperature is measured using a thermometer. Unlike our sense of touch, a thermometer provides accurate and reliable readings that can be understood by everyone.

Everyday Observation	Scientific Explanation
Tea feels hotter than water.	Tea has a higher temperature.
Ice feels very cold.	Ice has a much lower temperature.
Boiling water feels extremely hot.	Its temperature is much higher than room temperature.

Thermometer

A thermometer is an instrument used to measure temperature accurately. It converts changes in temperature into readable numerical values. Modern thermometers are easy to use, safe, and highly accurate.

Different thermometers are designed for different purposes. Choosing the correct thermometer is important because each type has a specific range and application.

Types of Thermometers

Several types of thermometers are used in daily life, hospitals, laboratories, and weather stations.

Type	Main Use	Special Feature
Clinical Thermometer	Human body temperature	Designed for medical use.
Digital Thermometer	Body temperature	Electronic display and quick reading.
Laboratory Thermometer	Scientific experiments	Wide temperature range.
Infrared Thermometer	Non-contact temperature measurement	Measures temperature from a distance.
Room Thermometer	Indoor air temperature	Shows surrounding air temperature.

Clinical Thermometer

A clinical thermometer is specially designed to measure the temperature of the human body. Nowadays, digital clinical thermometers are commonly used because they provide quick readings and do not contain harmful mercury.

The average normal body temperature of a healthy adult is 37°C, which is equal to 98.6°F. However, body temperature may vary slightly depending on age, physical activity, and time of the day.

Advantages of Digital Thermometers

Digital thermometers have become popular because they are safe, convenient, and easy to use.

• Provide fast readings.
• Easy to read digital display.
• Do not contain poisonous mercury.
• Suitable for children and elderly people.
• Reduce the risk of infection when used properly.

Precautions While Using a Clinical Thermometer

Following proper precautions ensures accurate readings and maintains hygiene.

• Wash the thermometer tip before and after use.
• Read the instruction manual carefully.
• Keep the electronic display away from water.
• Do not hold the thermometer by its sensing tip.
• Wait for the beep before taking the reading.

Laboratory Thermometer

A laboratory thermometer is used to measure the temperature of liquids and other substances during scientific experiments. It usually has a much wider temperature range than a clinical thermometer, making it suitable for measuring both very low and very high temperatures.

Most laboratory thermometers use coloured alcohol or mercury inside a narrow glass tube. As temperature changes, the liquid expands or contracts, causing the liquid column to rise or fall.

Correct Method of Using a Laboratory Thermometer

To obtain accurate measurements, the thermometer should be used correctly.

• Keep the thermometer in a vertical position.
• Immerse only the bulb in the liquid.
• Do not allow the bulb to touch the sides or bottom of the container.
• Read the temperature while the thermometer is still immersed.
• Take the reading at eye level to avoid errors.

Temperature Scales

Scientists use different scales to express temperature. Although they measure the same quantity, each scale has different reference points.

Scale	Unit	Common Use
Celsius	°C	Most commonly used in schools and daily life.
Fahrenheit	°F	Used in some countries.
Kelvin	K	Scientific research and SI unit.

Relationship Between Temperature Scales

Different temperature scales can represent the same temperature using different numerical values.

Celsius	Fahrenheit	Kelvin
37°C	98.6°F	310.15 K
0°C	32°F	273.15 K

To convert Celsius into Kelvin:

Temperature (K) = Temperature (°C) + 273.15

Air Temperature

Air temperature is the temperature of the surrounding atmosphere. It changes throughout the day due to sunlight, clouds, rainfall, wind, and seasons. Weather stations continuously measure air temperature to prepare weather forecasts.

Daily weather reports generally mention the maximum and minimum air temperatures recorded during the day.

Applications of Temperature Measurement

Temperature measurement plays an important role in almost every field of life.

• Diagnosing fever and monitoring health.
• Performing laboratory experiments.
• Preparing weather forecasts.
• Maintaining food safety and refrigeration.
• Industrial manufacturing processes.
• Agricultural planning.
• Environmental monitoring.
• Cooking and food processing.
• Renewable energy research.
• Scientific investigations.

Importance of Accurate Temperature Measurement

Accurate temperature measurement helps doctors diagnose illnesses correctly, enables scientists to perform reliable experiments, assists industries in maintaining product quality, and supports weather forecasting. Incorrect temperature readings may lead to wrong conclusions and unsafe situations.

Remember These Points

The following points are useful for quick revision before examinations.

• Temperature measures the degree of hotness or coldness of a body.
• Our sense of touch cannot accurately determine temperature.
• A thermometer is used to measure temperature.
• Clinical thermometers measure body temperature.
• Laboratory thermometers are used for scientific experiments.
• The normal body temperature of a healthy adult is about 37°C or 98.6°F.
• The SI unit of temperature is kelvin (K).
• Digital thermometers are safer than mercury thermometers.
• Always read a laboratory thermometer while it is immersed in the liquid.
• Weather stations regularly measure air temperature for weather forecasting.

Chapter Summary

Temperature is one of the most useful physical quantities in science and everyday life. It helps us compare the hotness or coldness of different objects accurately. Since our sense of touch cannot always judge temperature correctly, thermometers are used for reliable measurements. Clinical thermometers measure human body temperature, while laboratory thermometers are used in scientific experiments. Temperature can be expressed using the Celsius, Fahrenheit, or Kelvin scales. Accurate temperature measurement is essential in healthcare, scientific research, industries, agriculture, weather forecasting, and many other fields. Understanding the correct use of thermometers and temperature scales enables students to apply scientific knowledge confidently in both classroom activities and daily life.

Chapter 7. Temperature and its Measurement

Chapter 7. Temperature and its Measurement

This assignment is designed according to the latest CBSE competency-based assessment pattern. It includes objective, subjective, case-based, and Higher Order Thinking Skills (HOTS) questions to help students revise the chapter thoroughly and strengthen their conceptual understanding.

Assignments – What Have You Learned?

Attempt all the following questions without referring to your textbook. This worksheet will help you improve your knowledge, application skills, and examination confidence.

Part A: Fill in the Blanks

Complete the following statements using the correct words.

1. Temperature is the measure of the __________________ of a body.
2. A __________________ is used to measure temperature.
3. The SI unit of temperature is __________________.
4. The average normal human body temperature is __________________ °C.
5. A __________________ thermometer is used to measure body temperature.
6. A laboratory thermometer usually has a range from __________________ to __________________.
7. Digital thermometers use __________________ sensors.
8. The symbol of degree Celsius is __________________.
9. Air temperature is recorded at __________________ stations.
10. Mercury thermometers are being replaced because mercury is __________________.

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Part B: True or False

Write True or False for each statement.

1. Our sense of touch can always measure temperature accurately.
2. The SI unit of temperature is kelvin.
3. Clinical thermometers are mainly used in hospitals.
4. Laboratory thermometers are suitable for measuring body temperature.
5. Digital thermometers are safer than mercury thermometers.
6. 37°C is equal to 98.6°F.
7. The bulb of a laboratory thermometer should touch the bottom of the beaker.
8. Weather reports mention maximum and minimum air temperatures.
9. Infrared thermometers measure temperature without touching the body.
10. Temperature helps us compare the hotness or coldness of objects.

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Part C: Match the Following

Match Column A with the correct answer in Column B.

Column A	Column B
1. Clinical Thermometer	(a) SI unit of temperature
2. Kelvin	(b) Measures body temperature
3. Laboratory Thermometer	(c) Weather forecasting
4. Air Temperature	(d) Scientific experiments
5. Digital Thermometer	(e) Uses electronic heat sensors

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Part D: One Word Answer

Answer each question in one word or one term.

1. Which instrument measures temperature?
2. Which thermometer measures body temperature?
3. What is the SI unit of temperature?
4. Which scale uses the symbol °F?
5. Which thermometer measures temperature without touching the body?

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Part E: Very Short Answer Questions

Answer the following questions in one or two sentences.

1. What is temperature?
2. Why is a thermometer used instead of our sense of touch?
3. State the normal body temperature of a healthy adult.
4. Name the three temperature scales.
5. What is the function of a digital thermometer?

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Part F: Short Answer Questions

Answer the following questions in about 30–50 words.

1. Differentiate between a clinical thermometer and a laboratory thermometer.
2. Write any four precautions while using a laboratory thermometer.
3. Explain why mercury thermometers are being replaced by digital thermometers.
4. Why does body temperature vary slightly among healthy people?
5. Explain why air temperature changes during different seasons.

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Part G: Long Answer Questions

Answer the following questions in detail.

1. Explain the working and uses of different types of thermometers.
2. Describe the correct procedure for measuring temperature using a laboratory thermometer.
3. Explain the importance of accurate temperature measurement in healthcare, science, and daily life.
4. Compare the Celsius, Fahrenheit, and Kelvin temperature scales.
5. Why is it important to follow safety precautions while using thermometers? Explain with suitable examples.

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Part H: Case Study Questions

Read the passage carefully and answer the questions that follow.

Riya returned home after playing outside on a hot summer afternoon. She felt tired and thought she had a fever. Her mother cleaned a digital thermometer, placed it under Riya's tongue, and waited for the beep. The thermometer showed 37°C. Her mother explained that this was the normal body temperature and advised Riya to drink water and rest for some time.

Answer the following questions:

1. Which instrument was used to measure Riya's body temperature?
2. What was the temperature reading?
3. Is 37°C considered a normal body temperature?
4. Why should the thermometer be cleaned before and after use?
5. Why should we not judge fever only by touching a person's forehead?

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Part I: Competency-Based Questions

Apply your understanding of the chapter to answer the following questions.

1. Your friend says that touching a glass of water is enough to know its exact temperature. Do you agree? Give reasons.
2. A student removes a laboratory thermometer from hot water before reading it. Will the reading be accurate? Explain.
3. Why are infrared thermometers useful in hospitals during infectious disease outbreaks?
4. How does accurate temperature measurement help weather scientists?
5. Why should different thermometers be used for different purposes?

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Part J: HOTS (Higher Order Thinking Skills)

Think carefully and answer the following questions.

1. If two objects feel equally warm to your hand, can you conclude that both have the same temperature? Explain your answer.
2. Suppose digital thermometers were not available. What safety problems might arise from using mercury thermometers?
3. Why do scientists prefer numerical temperature measurements instead of simply describing objects as hot or cold?
4. A laboratory thermometer accidentally touches the bottom of a beaker while measuring hot water. How might this affect the reading?
5. Explain why accurate temperature measurement is important in hospitals, laboratories, industries, weather forecasting, and food storage.

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Self-Assessment Checklist

Tick (✔) the statements that are true for you after completing this chapter.

• ☐ I can explain the meaning of temperature.
• ☐ I can identify different types of thermometers.
• ☐ I know the SI unit of temperature.
• ☐ I can compare Celsius, Fahrenheit, and Kelvin scales.
• ☐ I know the correct method of using a laboratory thermometer.
• ☐ I understand the precautions while using thermometers.
• ☐ I can solve competency-based and case study questions.
• ☐ I am confident about this chapter for my CBSE examination.