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Chapter 7 Temperature and its Measurement Wrong measurements are worse than no measurements at all....

Chapter 7 Temperature and its Measurement Wrong measurements are worse than no measurements at all. — Anna Mani Lambok and his elder sister Phiban live in Shillong. One day they came home from school. Their parents were away at work and Lambok complained that he was feeling feverish. Phiban touched his forehead and felt that he might be having a fever. To confirm this, she took out the thermometer kept in the almirah. She washed its tip with soap and water, and measured Lambok’s temperature. To her relief, she found that his temperature was normal. She washed the thermometer tip again, dried it and put it back. She then asked Can it always be ? Lambok to change his school correctly judged, that uniform, eat his lunch, and rest for a person has fever, some time. only by touching the person? 7.1 Hot or Cold? We know from experience that some bodies are hotter than others. For example, during summers, the tap water may be hotter than the cold water from a matka (earthen pot) or a Chapter 7.indd 123 10-07-2024 12:50:47  refrigerator. We can realise this by merely touching the two samples of water. But can we always rely upon our sense of touch? Let us find out. Activity 7.1: Let us investigate ‹‹ Take three large containers and label them A, B and C, as shown in Fig. 7.1. ‹‹ Pour warm water in container A, tap water in B and ice- cold water in C. ‹‹ We will conduct this activity in two parts — prediction and observation. ‹‹ Firstly, predict what will you feel if you —— dip your right hand in A and left hand in C and keep them there for 1–2 minutes. —— take out your hands from containers A and C, and place both hands simultaneously in B. A B C A B C Curiosity | Textbook of Science| Grade 6 Fig. 7.1: Feeling hotness or coldness of water by dipping hands ‹‹ Write down your predictions. —— What will my right hand feel on dipping in B? —— What will my left hand feel on dipping in B? ‹‹ Now, conduct the activity and write your observations. 124 Chapter 7.indd 124 10-07-2024 12:50:48  Compare whether your observations match with your predictions. Did your right hand feel that the water in container B is cool, while your left hand felt that the same water is warm? What do you infer from these observations? Then how do we find out how hot We cannot always rely upon our sense of or cold a body touch to decide correctly whether a body is is? hot or cold. 7.2 Temperature A reliable measure of hotness (or coldness) of a body is its temperature. A hotter body has a higher temperature than a colder body. The difference in temperature between the two bodies tells us how hot a body is in comparison to another body. A device that measures temperature is called a thermometer. There are two kinds of thermometers that you are likely to come across—clinical thermometers and laboratory thermometers. Clinical thermometers are used to measure human body temperatures whereas laboratory thermometers are used for many other purposes. Let us now learn more about thermometers and how to use them to measure temperature. 7.3 Measuring Temperature 7.3.1 Clinical thermometer You might be familiar with a thermometer, like that shown in Fig. 7.2, which is used for measuring our body temperature. It is called a clinical thermometer. Such thermometers show Temperature and its Measurement temperatures digitally. These are also known as digital clinical thermometers and run on batteries. These measure Tip Fig.7.2: A digital clinical thermometer 125 Chapter 7.indd 125 10-07-2024 12:50:49  temperature when the thermometer is placed in contact with a person’s body. For measuring temperature, the clinical thermometers generally use a scale called the Celsius scale. On this scale, the unit of temperature is degree Celsius and is denoted by °C. Earlier, mercury thermometers were used for measuring the body temperature. But mercury is an extremely toxic substance and is difficult to dispose of if the thermometer breaks accidently. Digital thermometers pose no such risk and also the numbers in its display are easier to read. Therefore, mercury thermometers are being replaced by digital thermometers. Temperature in a digital thermometer is determined with the help of heat sensors. Dur Do you pand ing the C know? ther emic, so OVID-19 m me s whic ometer h co s we pecial temp uld m re us from e ra ture e a sure ed, a dis o th tanc f a pers e e. on thos What w e? ere Curiosity | Textbook of Science| Grade 6 They are non-contact thermometers, also called infrared thermometers. Such thermometers can measure temperature without touching a person’s body and thus reduce the risk of spreading disease. 126 Chapter 7.indd 126 10-07-2024 12:50:58  Activity 7.2: Let us measure Let us now use a digital clinical thermometer to measure body temperature. You may measure your own temperature as well as Precautions the temperature of some of your friends. to be taken while Talk to your friends to find out who would using a digital clinical be willing to get their body temperatures thermometer measured by you. To be used after reading the ‹‹ Wash your hands and the tip of the instruction manual of the digital thermometer with soap and thermometer. water. Tip of the thermometer to ‹‹ Reset the thermometer by pressing the be washed with soap and reset button. water before and after use. ‹‹ Place the thermometer under the While washing, care to be taken to keep the digital tongue and close your mouth. portion such as the display ‹‹ Wait till the thermometer makes a out of water. beeping sound or flashes a light. Do not hold the thermometer ‹‹ Take it out from the mouth and read by the tip. the temperature on the digital display. ‹‹ Record the temperature in Table 7.1. ‹‹ Clean the tip of the thermometer with soap and water, and dry it. ‹‹ Repeat the above steps for measuring the temperatures of your friends. Table 7.1: Body temperatures of 10 persons Temperature and its Measurement S. no. Name Temperature (°C) 1.... 10 127 Chapter 7.indd 127 10-07-2024 12:50:59  The normal temperature of a healthy human body is taken to be 37.0 °C. But in this activity, did you find that the normal temperature of every person was 37.0 °C? Or did you find the temperature slightly higher or lower for some people? The temperature of every person may not be 37.0 °C. What we call normal temperature ? Do small children is the average body temperature of a large generally have number of healthy people. A perfectly slightly higher body healthy person may, therefore, have a temperatures as normal temperature slightly different from compared to adults? 37.0 °C. The body temperature is influenced by several factors, such as age, time of the day and activity level. ? Do old people, even You may try measuring your own when healthy, generally temperature at different times of the day and have lower body on different days. Record the thermometer temperatures than readings in your notebook. After a month, young adults? analyse your temperature record and see if there are any variations. If yes, try to think what might be the reasons for that. I have seen The temperature of human beings does a friend of not normally go below 35 °C or above 42 °C. using a dig m ital thermo ine For measuring the body temperature that reads meter temperatu a different re on of small children or old people, the digital scale. It sh the norma ows thermometer can also be placed in the l temperatu a healthy h re of armpit. The temperature measured this way uman bod 98.6 °F. W y as hat is the r eason is about 0.5 °C to 1 °C lower than the actual for this diff body temperature. erence? There is another scale of temperature Curiosity | Textbook of Science| Grade 6 known as Fahrenheit scale. On this scale, the unit of temperature is degree Fahrenheit and is denoted by °F. A temperature measured as 37.0 °C on Celsius scale is equivalent to 98.6 °F on Fahrenheit scale. The Fahrenheit scale is not used in most scientific studies anymore. In scientific work, there is another scale of temperature known as Kelvin scale. On this scale, the unit for temperature is kelvin and is denoted by K. The SI unit of temperature 128 is kelvin. Chapter 7.indd 128 10-07-2024 12:50:59  All three temperature We can easily convert the scales, Celsius, Fahrenheit temperature from Celsius scale to and Kelvin are named in Kelvin scale by using: honour of the scientists who Temperature in Kelvin developed these scales. scale = Temperature in Celsius scale + 273.15 More to The names of temperature scales—Celsius scale, know! Fahrenheit scale and Kelvin scale—start with a capital letter. For the units for temperature, deg ree Celsius and degree Fahrenheit, the word degree starts with a lower-case letter while Celsius and Fahrenheit start with a capital letter. The unit kelvin starts with a lower-case letter. The symbols of all units (°C, °F, K) are capital letters. Note that degree sign (°) is not written with K. A full stop is not written after the symbol, except at the end of a sentence. While writing the temperature, a space is left between the number and the unit. For temperatures more than one degree, use the plural of ‘degree’, that is, ‘degrees’, while writing the full form of the unit. How was fever detected before ? ? Fever Can a clinical thermometers were developed. This thermometer be affects the pulse rate of a person used for measuring was known even in olden days the temperature of in India. However, apart from boiling water? Or fever, some other situations for measuring the also affect the pulse rate. temperature of ice? Hence, pulse rate alone is not Temperature and its Measurement Do you a reliable indicator of fever. know? No, the temperatures of boiling water and ice are outside the How can we measure range of a clinical temperatures beyond thermometer. the range of a clinical thermometer? 129 Chapter 7.indd 129 10-07-2024 12:51:41  7.3.2 Laboratory thermometer There are many types of laboratory thermometers but the one that might be available in your school laboratory may look like the one shown in Fig. 7.3a. It consists of a long, narrow, uniform glass tube which is sealed. At one end of the tube is a bulb which contains a liquid. Outside the bulb, in the tube, a narrow column of liquid can be seen. There is a Celsius scale marked along the tube. The liquid column rises or falls with change in temperature. The mark of the Celsius scale with which the top level of the liquid column coincides is the temperature reading. The liquid used in the laboratory thermometer is generally alcohol (coloured red to make it easily seen) or mercury. Do you know? Activity 7.3: Let us observe Let us try to find the temperature range of a given laboratory thermometer. ‹‹ Take a laboratory thermometer and observe it carefully. Precautions ‹‹ Note down the following: to be taken while using a laboratory —— What is the lowest thermometer temperature it Curiosity | Textbook of Science| Grade 6 Handle with care. If can measure? it hits against some Bulb hard object, it can —— What is the highest break. temperature it Do not hold it by the can measure? bulb. Fig.7.3(a): A laboratory —— So, the range of this thermometer thermometer is Now look at the thermometer shown in Fig. 7.3a carefully. Can you tell its range? Its range is from –10 °C to 110 °C. 130 Chapter 7.indd 130 10-07-2024 12:51:59  Activity 7.4: Let us observe and calculate Let us now try to find the smallest value that a given laboratory thermometer can read. ‹‹ Again, take the same laboratory thermometer which you used in Activity 7.3 and observe it carefully. ‹‹ Note down the following: —— How much is the temperature difference indicated between the two bigger marks? —— How many divisions (shown by smaller marks) are there between these two bigger marks? —— How much temperature does one small division indicate? —— So, the smallest value that the thermometer can read is Fig. 7.3b shows a closeup of a part of the thermometer shown in Fig. 7.3a. Can you now find the smallest value that this thermometer can read? For the thermometer shown in Fig. 7.3b, the temperature difference indicated between 0 °C and 10 °C or between 10 °C and 20 °C is 10 °C. And the number of divisions between these marks are 10 divisions. So, one small division can read 10/10 = 1 °C. That is, the smallest value that this thermometer can read is 1 °C. Your school laboratory may have thermometers for which the range and the value of the smallest division Temperature and its Measurement may be different. It is, therefore, always necessary to look carefully at the thermometer you are about to use. You have learnt how to find the temperature range of a given laboratory thermometer. You have also learnt how to find the smallest value that Fig. 7.3(b): a given laboratory thermometer can read. We Closeup of a will now learn how to measure temperature part of the using a laboratory thermometer. But, let us first thermometer learn how to use a laboratory thermometer shown in Fig. 7.3a. correctly. 131 Chapter 7.indd 131 10-07-2024 12:51:59  Correct way of measuring temperature using a laboratory thermometer ‹‹  hen the thermometer W is immersed in water, its bulb should not touch the bottom or the sides of the beaker. ‹‹ The thermometer should be held vertically (Fig. 7.4). It Closeup of a part of laboratory thermometer should not be tilted. Laboratory thermometer ‹‹ The temperature must be read while Beaker the thermometer is Warm water immersed in water. Fig.7.4: Measuring temperature of warm water ‹‹  W hile reading the thermometer, the eye should be directly in line with the level of the liquid column to be read (Fig. 7.4). Activity 7.5: Let us measure ‹‹ Take some warm water in a beaker. ‹‹ Dip the thermometer in water so that the bulb is immersed in water (Fig. 7.4). ‹‹ Observe the rise of liquid column in the thermometer. Wait till the column stops rising and note the Curiosity | Textbook of Science| Grade 6 Can se temperature (do not wait too long; otherwise, u y we rator for the water itself will start to cool). bo ter What is the temperature of water a la ome body rm ng fa measured by you? Compare it with the the asuri ure o me perat n? readings of your friends. o tem pers Do you notice that, as soon as you take the thermometer out of the water, the level of liquid column begins to fall? This means that the temperature must be read while the thermometer is immersed in water. 132 Chapter 7.indd 132 10-07-2024 12:52:00  Following two experimental setups are to be arranged by your teacher. One by one, as per your turn, go closer to the setups and observe the readings of both the thermometers. What are the temperatures of ice and boiling water? More to do! Laboratory thermometer Boiling Laboratory water thermometer Burner Crushed ice Caution This activit y should be performed strictly Read the temperatures of ice and boiling water again after only unde r supervisio some time. Are the temperatures same or have changed? You n of the teache may have noticed that the temperature of water remains r. Do not touch constant while it is boiling. Also, the temperature of ice the experimen remains constant while it is melting. tal setups. Activity 7.6: Let us compare ‹‹ Phiban’s Science teacher arranged the experimental setup for measuring temperature of boiling water. The temperature readings of the boiling water taken by Phiban and her classmates in Shillong are given in Table 7.2. Table 7.2: Temperature of boiling water Temperature and its Measurement Temperature of boiling Name water (in °C) Phiban 97.8 Shemphang 98.0 Onestar 97.9 Kloi 98.0 Bandarisha 98.1 133 Chapter 7.indd 133 10-07-2024 12:52:15  ‹‹ Compare the temperatures of boiling water recorded by different students. Why are there differences in their readings? Discuss the possible reasons amongst yourselves. Maybe, the correct way of reading temperature was not followed by all the students. 7.3.3 Air temperature You might have seen thermometers, such as the one shown in Fig. 7.5, hung on walls of your school laboratory, doctor’s clinic, and hospitals. These give an approximate idea of the room temperature. Have you seen weather reports in newspapers, TV news or internet? These reports also mention the maximum and minimum air temperature of the day. Fig.7.5: Room thermometer Activity 7.7: Let us analyse ‹‹ Read or listen to the weather reports for a place for 10 successive days. ‹‹ Record the maximum and minimum air temperature for each day in Table 7.3. ‹‹ Analyse the data in the Table 7.3. Curiosity | Textbook of Science| Grade 6 Table 7.3: Maximum and minimum air temperature Maximum air Minimum air S.no. Date temperature temperature 1... 134 10. Chapter 7.indd 134 10-07-2024 12:52:16  Does the maximum and minimum temperature stay at the same level during these days? Because weather depends on several factors, these temperatures usually vary every day. Generally, as we approach the summer season, the temperature rises and during the winter season it falls. There are many techniques for measuring air temperature. Air temperature is an important weather parameter and is More to monitored at weather stations all over know! the world. The data gathered on air temperature along with various other parameters are used for making weather forecasts. Anna Mani (1918–2001) was an Indian scientist, also known as the ‘Weather Woman of India’. She invented and built a large number of weather measurement instruments. Temperature and its Measurement This reduced the reliance of India on other nations for such instruments. She also explored the possibilities of using wind and solar energy in India. Her work helped India to become one of the global leaders in renewable energy. 135 Chapter 7.indd 135 10-07-2024 12:52:30  Keywords Air Temperature Analyse Celsius Scale Calculate Clinical thermometer Compare degree Celsius Discuss degree Fahrenheit Infer Fahrenheit scale Investigate kelvin Measure Kelvin scale Observe Laboratory thermometer Precaution SI unit of temperature Predict Temperature Record Summary Curiosity | Textbook of Science| Grade 6 ‹‹ The temperature of a body tells us how hot or cold it is. ‹‹ The three most-used scales of temperature are: (a) the Celsius scale, (b) the Fahrenheit scale, and (c) the Kelvin scale. The units of temperature in these scales are (a) degree Celsius, denoted by °C, (b) degree Fahrenheit, denoted by °F, and (c) kelvin, denoted by K. ‹‹ The SI unit for temperature is kelvin. ‹‹ A clinical thermometer is used for measuring body temperature. ‹‹ Normal temperature of a healthy human adult is taken to be 37.0 °C or 98.6 °F. ‹‹ Laboratory thermometers typically have a temperature range 136 from –10 °C to 110 °C. Chapter 7.indd 136 10-07-2024 12:52:36  Let us enhance our learning 1. The normal temperature of a healthy human being is close to. (i) 98.6 °C (ii) 37.0 °C (iii) 32.0 °C (iv) 27.0 °C 2. 37 °C is the same temperature as. (i) 97.4 °F (ii) 97.6 °F (iii) 98.4 °F (iv) 98.6 °F 3. Fill in the blanks: (i) The hotness or coldness of a system is determined by its. (ii) The temperature of ice-cold water cannot be measured by a thermometer. (iii) The unit of temperature is degree. 4. The range of a laboratory thermometer is usually. (i) 10 °C to 100 °C (ii) –10 °C to 110 °C (iii) 32 °C to 45 °C (iv) 35 °C to 42 °C 5. Four students used a laboratory thermometer to measure the temperature of water as shown in Fig. 7.6: Temperature and its Measurement Student 1 Student 2 Student 3 Student 4 137 Fig. 7.6 Chapter 7.indd 137 10-07-2024 12:52:40  Who do you think followed the correct way for measuring temperature? (i) Student 1 (ii) Student 2 (iii) Student 3 (iv) Student 4 6. Colour to show the red column on the drawings of thermometers (Fig. 7.7) as per the temperatures written below: 14 °C 17 °C 7.5 °C Fig. 7.7 7. Observe the part of thermometer shown in Fig. 7.8 and answer the following questions: Curiosity | Textbook of Science| Grade 6 Fig. 7.8 (i) What type of thermometer is it? (ii) What is the reading of the thermometer? (iii) What is the smallest value that this thermometer can measure? 8. A laboratory thermometer is not used to measure our body temperature. Give a reason. 138 Chapter 7.indd 138 10-07-2024 12:52:42  9. Vaishnavi has not gone to school as she is ill. Her mother has kept a record of her body temperature for three days as shown in Table 7.4. Table 7.4: Body temperature record of Vaishnavi Temperature at DAY 7am 10am 1pm 4pm 7pm 10pm One 38.0 °C 37.8 °C 38.0 °C 38.0 °C 40.0 °C 39.0 °C Two 38.6 °C 38.8 °C 39.0 °C 39.0 °C 39.0 °C 38.0 °C Three 37.6 °C 37.4 °C 37.2 °C 37.0 °C 36.8 °C 36.6 °C (i) What was Vaishnavi’s highest recorded temperature? (ii) On which day and at what time was Vaishnavi’s highest temperature recorded? (iii) On which day did Vaishnavi’s temperature return to normal? 10. If you have to measure the temperature 22.5 °C, which of the following three thermometers will you use (Fig. 7.9)? Explain. Temperature and its Measurement (a) (b) (c) Fig. 7.9: Three thermometers 139 Chapter 7.indd 139 10-07-2024 12:52:43  11. The temperature shown by the thermometer in Fig. 7.10 is (i) 28.0 °C (ii) 27.5 °C (iii) 26.5 °C (iv) 25.3 °C Fig. 7.10 12. A laboratory thermometer has 50 divisions between 0 °C and 100 °C. What does each division of this thermometer measure? 13. Draw the scale of a thermometer in which the smallest division reads 0.5 °C. You may draw only the portion between 10 °C and 20 °C. 14. Someone tells you that she has a fever of 101 degrees. Does she mean it on the Celsius scale or Fahrenheit scale? Learning further ‹‹ Gather information from the Internet and find out how the body temperature of animals, such as a cat, dog, horse, camel, cow and buffalo, is measured. If there is any veterinary hospital in your vicinity, you may visit to see the body temperature of animals being measured. ‹‹ Find out which places in India are usually regarded to be the coldest and hottest. Also, find out the minimum and the maximum temperatures recorded for these places. ‹‹ Various planets in our Solar System are at different distances Curiosity | Textbook of Science| Grade 6 from the Sun. Search the Internet and make a table with the planets, their distances from the Sun (in increasing order) and their temperatures written. Does the average temperature of planets decrease as their distance from the Sun increases? If it is not true for any planet, find out for which planet and why. ‹‹ Hang a room thermometer in your classroom. Set up the apparatus, as shown in Fig. 7.11, near the thermometer hung on the wall. Take the readings of thermometers 1 and 2 three times during the day, say, first period, lunch break, and last period. 140 Chapter 7.indd 140 10-07-2024 12:52:48  Record your readings. Compare the readings and draw your conclusions. Repeat this for two weeks. Thermometer 1 (Room thermometer) Thermometer 2 (Laboratory thermometer) Beaker Water Fig. 7.11: Set up to measure temperature of water and room temperature The temperature at the core of the Sun reaches as high as 15 million degrees Celsius. Are More to there objects in the sky that have even higher know! temperatures? There is no limit on the highest temperature that can exist. However, as per Temperature and its Measurement scientific understanding, there is a limit to the lowest temperature that can be achieved. It is close to –273.15 °C (0 kelvin) and is called absolute zero. 141 Chapter 7.indd 141 10-07-2024 12:53:05  Notes Chapter 7.indd 142 10-07-2024 12:53:05