CBSE Class 6- Science Chapter 7: Temperature and its Measurement- Study Notes (PDF)

Study Notes: Temperature and its Measurement (Class 6-NCERT(Curiosity) Science

1. Understanding Hot, Cold, and Temperature

1.1 The Unreliability of Touch

Our sense of touch can be misleading when determining if something is hot or cold. An object’s perceived temperature can depend on our prior sensory experience.

• Demonstration (Activity 7.1): An experiment involving three containers of water—one warm (A), one tap water (B), and one ice-cold (C)—illustrates this principle.
  • Placing one hand in warm water (A) and the other in ice-cold water (C) for a few minutes adapts the hands to different temperatures.
  • When both hands are then simultaneously placed in the container of tap water (B), the hand from the warm water feels that the tap water is cool, while the hand from the cold water feels that the same tap water is warm.
  • This confirms that the sense of touch is not a reliable method for accurately measuring temperature.

1.2 Defining Temperature

Temperature is the reliable and scientific measure of the hotness or coldness of a body. Key characteristics include:

• A hotter body has a higher temperature than a colder body.
• The difference in temperature between two bodies indicates how hot one is in comparison to the other.
• A thermometer is the device used to measure temperature.

2. Types of Thermometers and Their Uses

There are two primary kinds of thermometers discussed: clinical thermometers and laboratory thermometers.

2.1 Clinical Thermometers

These are specifically designed for measuring human body temperature.

• Digital Clinical Thermometers:
  • Modern standard for measuring body temperature.
  • They run on batteries and display the temperature digitally.
  • They work using heat sensors that measure temperature when the tip is in contact with the body.
  • Advantages over Mercury Thermometers: Mercury is a highly toxic substance, making disposal difficult and dangerous if a mercury thermometer breaks. Digital thermometers pose no such risk and are easier to read.
• Infrared (Non-Contact) Thermometers:
  • Used extensively during the COVID-19 pandemic.
  • These thermometers can measure a person’s temperature from a distance without physical contact.
  • This non-contact feature is crucial for reducing the risk of spreading infectious diseases.

2.2 Laboratory Thermometers

These are used for various scientific and general purposes, not for measuring body temperature.

• Structure: They typically consist of a long, narrow, uniform sealed glass tube with a bulb at one end containing a liquid (usually alcohol colored red, or mercury).
• Function: As the temperature changes, the liquid column in the tube rises or falls. The temperature is read from the marked Celsius scale where the top of the liquid column aligns.
• Typical Range: The common range for a laboratory thermometer is from –10 °C to 110 °C.

3. Temperature Scales

Three primary scales are used to measure temperature.

Scale	Unit	Symbol	Usage
Celsius	degree Celsius	°C	Commonly used in clinical thermometers and general scientific work.
Fahrenheit	degree Fahrenheit	°F	An older scale, no longer used in most scientific studies. 37.0 °C is equivalent to 98.6 °F.
Kelvin	kelvin	K	The SI unit of temperature, used in scientific work. The degree symbol (°) is not used with kelvin.

• Conversion: To convert from Celsius to Kelvin, the formula is:
  • Temperature in Kelvin (K) = Temperature in Celsius (°C) + 273.15
• Writing Conventions:
  • The names of the scales (Celsius, Fahrenheit, Kelvin) start with a capital letter.
  • The units degree Celsius and degree Fahrenheit start with a lower-case d, but kelvin is all lower-case.
  • Symbols (°C, °F, K) are always capitalized.
  • A space is left between the number and the unit symbol (e.g., 37.0 °C).

4. Measuring Temperature Correctly

4.1 Using a Digital Clinical Thermometer

• Precautions:
  1. Read the instruction manual before use.
  2. Wash the tip with soap and water before and after each use.
  3. Keep the digital display and battery portion away from water.
  4. Do not hold the thermometer by its tip.
• Procedure:
  1. Wash your hands and the thermometer tip.
  2. Press the reset button.
  3. Place the tip under the tongue and close the mouth.
  4. Wait for the beeping sound or flashing light.
  5. Remove and read the temperature from the digital display.

4.2 Using a Laboratory Thermometer

• Precautions:
  1. Handle with care to avoid breakage.
  2. Do not hold it by the bulb.
• Procedure for Measuring Liquid Temperature:
  1. Immerse the bulb in the liquid, ensuring it does not touch the bottom or sides of the container.
  2. Hold the thermometer vertically, not tilted.
  3. Read the temperature while the thermometer bulb is still immersed in the substance. The reading will fall quickly once removed.
  4. Position your eye directly in line with the level of the liquid column for an accurate reading.
• Reading the Scale:
  • Determine the range (highest and lowest measurable temperatures).
  • Determine the value of the smallest division by finding the temperature difference between two major marks and dividing by the number of smaller divisions between them. For example, if there are 10 divisions between 10 °C and 20 °C, each division represents 1 °C.

5. Key Temperature Concepts

5.1 Human Body Temperature

• The normal temperature for a healthy human adult is considered to be 37.0 °C (or 98.6 °F).
• This is an average temperature. A healthy person’s temperature can be slightly higher or lower.
• Factors influencing body temperature include age, time of day, and activity level.
• The human body temperature does not normally go below 35 °C or above 42 °C.
• When measured in the armpit, the reading is typically 0.5 °C to 1 °C lower than the actual body temperature.

5.2 Air Temperature

• Measured to get an idea of the room temperature or for weather reporting.
• Weather reports include the maximum and minimum air temperature for the day.
• Air temperature is a crucial weather parameter monitored at weather stations worldwide and is used for weather forecasting.

5.3 Extreme Temperatures

• Absolute Zero: The lowest possible temperature that can be achieved is 0 K (or approximately –273.15 °C).
• High Temperatures: There is no known upper limit to how high a temperature can be. The core of the Sun, for example, reaches about 15 million degrees Celsius.

5.4 Anna Mani (1918–2001)

• An Indian scientist known as the “Weather Woman of India.”
• She invented and built numerous weather measurement instruments, reducing India’s reliance on other nations.
• Her work in exploring wind and solar energy helped position India as a global leader in renewable energy.

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Quiz

Short-Answer Questions

(Answer in 2-3 sentences)

1. Why is our sense of touch not a reliable way to determine if an object is hot or cold?
2. What is temperature, and what device is used to measure it?
3. What are the two main types of thermometers discussed in the text?
4. What is the primary purpose of a clinical thermometer?
5. Why have digital thermometers largely replaced older mercury thermometers?
6. How do non-contact infrared thermometers help reduce the spread of disease?
7. What is the typical temperature range of a laboratory thermometer?
8. What is the normal body temperature of a healthy human adult in both Celsius and Fahrenheit?
9. List two factors that can cause a healthy person’s body temperature to vary from the 37.0 °C average.
10. Name the three scales of temperature mentioned in the text and their corresponding symbols.
11. What is the SI unit for temperature?
12. Describe the correct procedure for washing a digital clinical thermometer.
13. What happens to the liquid column in a laboratory thermometer when it is taken out of warm water?
14. What are two key precautions to take when handling a laboratory thermometer?
15. Explain how to determine the value of the smallest division on a laboratory thermometer.
16. Why can’t a clinical thermometer be used to measure the temperature of boiling water?
17. How should a laboratory thermometer be positioned in a beaker of water to get an accurate reading?
18. What is “absolute zero”?
19. Who was Anna Mani and what was her significant contribution to science in India?
20. In what context is air temperature measured and reported daily?
21. What is the correct way to write the unit for the Kelvin scale?
22. How is fever detected in olden days in India, and why was this method not entirely reliable?
23. What is the formula for converting a temperature from the Celsius scale to the Kelvin scale?
24. Where can a digital thermometer be placed to measure the temperature of small children, and how does this reading compare to the actual body temperature?
25. What did the students in Shillong measure, and why might their readings have differed?

Multiple-Choice Questions (MCQs)

1. A reliable measure of the hotness or coldness of a body is its: a) Weight b) Pressure c) Temperature d) Volume
2. What is the equivalent of 37.0 °C on the Fahrenheit scale? a) 96.8 °F b) 98.6 °F c) 37.0 °F d) 100 °F
3. The liquid used in a common laboratory thermometer is often: a) Water colored blue b) Pure mercury c) Alcohol colored red d) Saltwater
4. The SI unit of temperature is: a) degree Celsius b) degree Fahrenheit c) kelvin d) Centigrade
5. The normal temperature range for a human being is typically between: a) 30 °C and 40 °C b) 35 °C and 42 °C c) 25 °C and 35 °C d) 40 °C and 50 °C
6. When using a laboratory thermometer, the reading must be taken: a) After removing it from the substance b) While the bulb is still immersed in the substance c) By tilting the thermometer to see the scale clearly d) After shaking the thermometer vigorously
7. The temperature at the core of the Sun is approximately: a) 15 thousand degrees Celsius b) 1.5 million degrees Celsius c) 15 million degrees Celsius d) 150 million degrees Celsius
8. Anna Mani is also known as the: a) “Medical Woman of India” b) “Physics Woman of India” c) “Astronomy Woman of India” d) “Weather Woman of India”
9. Which of the following is a key precaution for using a digital clinical thermometer? a) Holding it firmly by the tip b) Washing the entire device under running water c) Washing the tip with soap and water before and after use d) Storing it near a heat source
10. The typical range of a laboratory thermometer is: a) 0 °C to 100 °C b) 35 °C to 42 °C c) –10 °C to 110 °C d) –50 °C to 50 °C
11. What type of thermometer was widely used during the COVID-19 pandemic for distance measurements? a) Mercury thermometer b) Digital clinical thermometer c) Laboratory thermometer d) Infrared thermometer
12. The lowest achievable temperature, known as absolute zero, is: a) 0 °C b) –273.15 °F c) 0 K d) –100 K
13. The main reason mercury thermometers are being replaced is that mercury is: a) Too expensive b) An extremely toxic substance c) Not accurate enough d) Hard to see in the tube
14. For an accurate reading with a laboratory thermometer, your eye should be: a) Above the liquid level, looking down b) Below the liquid level, looking up c) Directly in line with the liquid level d) At a comfortable angle to the thermometer
15. Temperature measured in an armpit is about ________ than the actual body temperature. a) 0.5 °C to 1 °C higher b) 0.5 °C to 1 °C lower c) Exactly the same d) 2 °C lower
16. A laboratory thermometer shows 10 divisions between the 20 °C and 30 °C marks. What is the value of one small division? a) 0.1 °C b) 0.5 °C c) 1 °C d) 2 °C
17. Which of these is NOT a correct way to write a temperature unit? a) 25 °C b) 300 K c) 72 °F d) 50° C
18. What physical parameter, besides fever, can affect a person’s pulse rate? a) Blood pressure b) Activity level and other situations c) Air temperature d) Height
19. Digital thermometers determine temperature using: a) Expanding liquid b) A bimetallic strip c) Heat sensors d) Infrared radiation
20. Weather reports typically mention the day’s: a) Average and median temperature b) Maximum and minimum air temperature c) Only the temperature at noon d) Ground temperature

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Answer Keys

Short-Answer Questions Answer Key

1. Our sense of touch is unreliable because our perception of temperature is relative and depends on what our skin has been exposed to previously. The three-container experiment shows that the same water can feel both warm and cool simultaneously to different hands.
2. Temperature is a reliable measure of how hot or cold a body is. It is measured using a device called a thermometer.
3. The two main types of thermometers discussed are the clinical thermometer, for measuring body temperature, and the laboratory thermometer, for various other purposes.
4. A clinical thermometer is designed specifically to measure human body temperature. Its range is limited to the temperatures typically found in the human body.
5. Digital thermometers have replaced mercury thermometers primarily because mercury is an extremely toxic substance. If a mercury thermometer breaks, disposal is difficult and hazardous, a risk that digital thermometers do not have.
6. Non-contact infrared thermometers can measure temperature from a distance without touching a person’s body. This prevents the transfer of germs and reduces the risk of spreading infectious diseases between people.
7. A common laboratory thermometer typically has a range from –10 °C to 110 °C. This wide range allows it to measure temperatures such as that of boiling water and ice.
8. The normal body temperature of a healthy human adult is taken to be 37.0 °C. This is equivalent to 98.6 °F on the Fahrenheit scale.
9. A healthy person’s body temperature can be influenced by several factors. Two such factors are the time of day and the person’s current activity level.
10. The three scales are the Celsius scale (°C), the Fahrenheit scale (°F), and the Kelvin scale (K).
11. The SI (Système International) unit for temperature is the kelvin, which is denoted by the symbol K.
12. To wash a digital clinical thermometer, its tip should be cleaned with soap and water. Care must be taken to keep the digital portion, such as the display, out of the water.
13. When a laboratory thermometer is taken out of warm water, the level of the liquid column begins to fall immediately. This is why the temperature must be read while the thermometer is still immersed.
14. Two key precautions for a laboratory thermometer are to handle it with care to prevent it from breaking against a hard object, and to not hold it by the bulb.
15. To find the value of the smallest division, first note the temperature difference between two bigger marks on the scale. Then, count the number of smaller divisions between them and divide the temperature difference by the number of divisions.
16. A clinical thermometer’s range is limited to human body temperatures (normally 35 °C to 42 °C). The temperature of boiling water (around 100 °C) is far outside this range and would break the thermometer.
17. To get an accurate reading, the thermometer should be held vertically in the beaker. Its bulb must be fully immersed in the water without touching the bottom or the sides of the container.
18. Absolute zero is the lowest possible temperature that can be achieved according to scientific understanding. It is equal to 0 kelvin or approximately –273.15 °C.
19. Anna Mani was an Indian scientist known as the “Weather Woman of India.” She invented and built many weather measurement instruments, which helped India become self-reliant and a leader in renewable energy.
20. Air temperature is measured and reported daily in weather reports, which typically mention the maximum and minimum air temperature for the day. This data is used for weather forecasting.
21. The unit for the Kelvin scale is written as “kelvin” (lower-case) and its symbol is K (capital). Unlike Celsius and Fahrenheit, the degree symbol (°) is not used with K.
22. In olden days, fever was sometimes detected by checking a person’s pulse rate, as fever can affect it. However, this was not entirely reliable because other situations besides fever can also affect the pulse rate.
23. The formula is: Temperature in Kelvin scale = Temperature in Celsius scale + 273.15.
24. For small children, the thermometer can be placed in the armpit. A temperature measured this way is typically about 0.5 °C to 1 °C lower than the actual body temperature.
25. The students in Shillong measured the temperature of boiling water. Their readings likely differed due to minor errors in measurement technique, such as not holding the thermometer vertically or not positioning their eye level with the liquid column.

Multiple-Choice Questions (MCQs) Answer Key

1. c) Temperature
2. b) 98.6 °F
3. c) Alcohol colored red
4. c) kelvin
5. b) 35 °C and 42 °C
6. b) While the bulb is still immersed in the substance
7. c) 15 million degrees Celsius
8. d) “Weather Woman of India”
9. c) Washing the tip with soap and water before and after use
10. c) –10 °C to 110 °C
11. d) Infrared thermometer
12. c) 0 K
13. b) An extremely toxic substance
14. c) Directly in line with the liquid level
15. b) 0.5 °C to 1 °C lower
16. c) 1 °C
17. d) 50° C
18. b) Activity level and other situations
19. c) Heat sensors
20. b) Maximum and minimum air temperature

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Essay Questions and Answers (For Teachers)

1. Explain in detail why our sense of touch is considered unreliable for measuring temperature. Use the experiment described in the source text to support your answer.

• Answer: Our sense of touch is an unreliable method for measuring temperature because it is subjective and relative, not absolute. The sensation of hot or cold depends on the temperature to which our skin has previously adapted. The experiment in Activity 7.1 demonstrates this perfectly. It uses three containers of water: warm (A), tap water (B), and ice-cold (C). When a person places one hand in the warm water and the other in the ice-cold water for a couple of minutes, the nerve endings in each hand adapt to these different temperatures. Subsequently, when both hands are placed into the container of room-temperature tap water, a contradictory sensation occurs. The hand that was in warm water now perceives the tap water as cool, while the hand that was in cold water perceives the same tap water as warm. This proves that our sense of touch cannot provide a consistent or objective measurement, leading to the conclusion that a calibrated instrument like a thermometer is necessary for a reliable measure of temperature.

2. Compare and contrast clinical thermometers and laboratory thermometers. Discuss their purpose, typical range, design, and correct usage.

• Answer: Clinical and laboratory thermometers are both devices for measuring temperature, but they are designed for different purposes and have distinct features.
  • Purpose: The primary purpose of a clinical thermometer is to measure human body temperature. A laboratory thermometer, in contrast, is used for a wide range of general scientific purposes, such as measuring the temperature of chemicals, water, or air in an experimental setup.
  • Range: This difference in purpose dictates their range. A clinical thermometer has a narrow range, typically from 35 °C to 42 °C, because human body temperature does not normally vary outside these limits. A laboratory thermometer has a much wider range, commonly from –10 °C to 110 °C, enabling it to measure phenomena like melting ice and boiling water.
  • Design: While modern clinical thermometers are typically digital and battery-operated, laboratory thermometers are often long glass tubes containing a column of colored alcohol or mercury that expands and contracts.
  • Usage: A digital clinical thermometer is placed under the tongue or in an armpit and the reading is taken after a beep. A laboratory thermometer must be held vertically with its bulb immersed in the substance (but not touching the container) and the reading must be taken while it is still immersed, as the liquid column falls quickly upon removal.

3. Describe the evolution from mercury thermometers to digital and infrared thermometers for clinical use. What were the driving factors for this change?

• Answer: The evolution of clinical thermometers has been driven by concerns for safety, ease of use, and hygiene. Initially, mercury thermometers were standard for measuring body temperature. However, mercury is an extremely toxic substance. If a glass mercury thermometer broke, it posed a significant health risk and created a hazardous waste disposal problem. This safety concern was the primary driver for change. Digital clinical thermometers were developed as a safer alternative. They operate using heat sensors, run on batteries, and provide a clear, easy-to-read digital display, eliminating the risks associated with mercury. More recently, especially during the COVID-19 pandemic, the infrared (or non-contact) thermometer became prominent. The main driver for its adoption was hygiene and the prevention of disease transmission. By measuring temperature from a distance without any physical contact, these thermometers minimize the risk of spreading pathogens from one person to another, making them ideal for screening large numbers of people in public spaces.

4. Detail the proper procedure and precautions for using a laboratory thermometer to measure the temperature of warm water in a beaker.

• Answer: To correctly measure the temperature of warm water with a laboratory thermometer, a specific procedure with several precautions must be followed.
  • Precautions: First, the thermometer must be handled with care to avoid breaking it. Second, it should never be held by the bulb, as the heat from your hand can affect the reading.
  • Procedure:
    1. The thermometer should be dipped into the warm water so that its bulb is fully immersed.
    2. It must be held vertically and not tilted. Crucially, the bulb must not touch the bottom or the sides of the beaker, as this would measure the temperature of the glass rather than the water.
    3. One must observe the liquid column rise and wait until it becomes stable.
    4. The temperature must be read while the thermometer’s bulb is still in the water, because the reading will begin to fall as soon as it is removed.
    5. For an accurate reading, the observer’s eye must be positioned directly in line with the top of the liquid column. Reading from an angle can cause a parallax error.

5. Discuss the three main temperature scales—Celsius, Fahrenheit, and Kelvin. Explain their units, symbols, and primary areas of application as described in the text.

• Answer: The source text describes three main scales for measuring temperature: Celsius, Fahrenheit, and Kelvin.
  • Celsius Scale: Its unit is the degree Celsius, denoted by the symbol °C. This scale is widely used for everyday purposes and in most scientific work, including in clinical and laboratory thermometers. For example, the normal human body temperature is 37.0 °C.
  • Fahrenheit Scale: Its unit is the degree Fahrenheit, denoted by °F. This is an older scale that is not used in most scientific studies anymore, though it is still in common use in some countries. The text notes that 37.0 °C is equivalent to 98.6 °F.
  • Kelvin Scale: Its unit is the kelvin (not degree kelvin), denoted by the symbol K. This is the official SI unit of temperature and is used primarily in scientific work. A key feature is that the degree symbol (°) is not used. The text provides a formula to convert from Celsius to Kelvin: K = °C + 273.15.

6. Explain what is meant by “normal body temperature” and discuss the factors that can cause it to vary among healthy individuals.

• Answer: The “normal body temperature” of 37.0 °C (or 98.6 °F) is not a fixed, universal value for every person at all times. Instead, it represents the average body temperature of a large number of healthy people. A perfectly healthy individual’s temperature may be slightly higher or lower than this average. The text identifies several factors that can influence body temperature, including age (small children may have slightly higher temperatures, while older people may have lower ones), the time of the day (temperature can fluctuate throughout a 24-hour cycle), and a person’s activity level. Therefore, a single temperature reading should be considered in context, as variations from the 37.0 °C average are common and not necessarily an indicator of illness.

7. Who was Anna Mani, and why is she a significant figure in the history of science in India?

• Answer: Anna Mani (1918–2001) was a distinguished Indian scientist who earned the nickname “Weather Woman of India.” Her significance stems from her pioneering work in meteorology and renewable energy. She invented and built a large number of weather measurement instruments. This was a crucial contribution because it reduced India’s reliance on importing such instruments from other nations, fostering scientific self-sufficiency. Furthermore, Anna Mani explored the potential of using wind and solar energy in India. Her foundational work in this area helped pave the way for India to become one of the world’s leaders in the field of renewable energy.

8. What is the importance of measuring maximum and minimum air temperatures, and how is this information utilized?

• Answer: Measuring the maximum and minimum air temperatures over a day is a fundamental practice in meteorology. This information, often seen in weather reports in newspapers or on TV, provides a snapshot of the daily temperature range for a specific location. Air temperature is a critical weather parameter. It is continuously monitored at weather stations all over the world. The data gathered on air temperature, along with various other parameters, is compiled and analyzed by meteorologists. This comprehensive dataset is then used to create weather forecasts, which are essential for agriculture, transportation, public safety, and daily planning.

9. Why is a laboratory thermometer unsuitable for measuring human body temperature?

• Answer: A laboratory thermometer is unsuitable for measuring human body temperature for two main reasons. First, its scale is not precise enough for clinical purposes. The smallest division on a typical laboratory thermometer might be 1 °C, which is too large an increment to accurately detect the subtle changes that indicate a fever. Second, and more importantly, the liquid column in a laboratory thermometer begins to fall very quickly as soon as it is removed from the substance being measured. To measure body temperature, the thermometer would have to be read while still in the person’s mouth, which is impractical and would lead to inaccurate readings as the person opens their mouth.

10. What is “absolute zero” and how does it relate to the Kelvin scale? Contrast this with the concept of a maximum possible temperature.

• Answer: “Absolute zero” is the theoretical lowest temperature that can be achieved. According to scientific understanding, it is the point at which all thermal motion of particles ceases. This temperature corresponds to 0 on the Kelvin scale (0 K), which is equivalent to –273.15 °C. The Kelvin scale is an absolute temperature scale because its zero point is absolute zero. In stark contrast, the text states that there is no known limit on the highest temperature that can exist. While phenomena like the core of the Sun reaching 15 million degrees Celsius are incredibly hot, they do not represent an upper boundary, and even higher temperatures are believed to exist elsewhere in the universe.

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Glossary of Key Terms

• Absolute Zero: The lowest temperature that can be achieved, corresponding to 0 K or approximately –273.15 °C.
• Air Temperature: The temperature of the air, an important weather parameter used for weather forecasts. Weather reports typically mention the maximum and minimum air temperature of the day.
• Celsius Scale: A common scale for measuring temperature, where the unit is degree Celsius (°C).
• Clinical Thermometer: A device used specifically for measuring human body temperature.
• degree Celsius (°C): The unit of temperature on the Celsius scale.
• degree Fahrenheit (°F): The unit of temperature on the Fahrenheit scale.
• Digital Clinical Thermometer: A modern, battery-operated thermometer that uses heat sensors to measure body temperature and displays the reading digitally.
• Fahrenheit Scale: A scale of temperature where the unit is degree Fahrenheit (°F). It is not commonly used in scientific work.
• Infrared Thermometer: A type of non-contact thermometer that can measure temperature from a distance, reducing the risk of spreading disease.
• kelvin (K): The unit of temperature on the Kelvin scale and the SI unit for temperature.
• Kelvin Scale: A scientific scale of temperature where the unit is the kelvin (K). Its zero point is absolute zero.
• Laboratory Thermometer: A thermometer used for various scientific purposes, typically with a wide range from –10 °C to 110 °C.
• Mercury Thermometer: An older type of thermometer that used the expansion and contraction of the toxic liquid metal mercury to indicate temperature.
• SI unit of temperature: The standard international unit for temperature, which is the kelvin (K).
• Temperature: A reliable measure of the hotness or coldness of a body.
• Thermometer: A device used to measure temperature.