Welcome dear students! Today we are going to learn about Temperature and its Measurement from Class 6 Science. Wrong measurements are worse than no measurements at all. This wise quote is by 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 Lambok to change his school uniform, eat his lunch, and rest for some time. Now, let us think. Can it always be correctly judged that a person has fever, only by touching the person? Let us find out.
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Section seven point one, 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, which is an earthen pot, or a 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 through an activity. Activity seven point one, Let us investigate. Take three large containers and label them A, B and C, as shown in Figure seven point one. Pour warm water in container A, tap water in container B, and ice cold water in container C. We will conduct this activity in two parts, prediction and observation. Firstly, predict what you will feel if you dip your right hand in A and left hand in C and keep them there for one to two minutes. Then, take out your hands from containers A and C, and place both hands simultaneously in B. Write down your predictions. What will my right hand feel on dipping it in B? What will my left hand feel on dipping it in B? Now, conduct the activity and write your observations. 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? We cannot always rely upon our sense of touch to decide correctly whether a body is hot or cold. Then how do we find out how hot or cold a body is?
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Section seven point two, 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.
Section seven point three point one, Clinical thermometer. You might be familiar with a thermometer, like that shown in Figure seven point two, which is used for measuring our body temperature. It is called a clinical thermometer. Such thermometers show temperatures digitally. These are also known as digital clinical thermometers and run on batteries. These measure 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 accidentally. 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.
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Do you know? During the COVID nineteen pandemic, some special thermometers were used, which could measure the temperature of a person from a distance. What were those? 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.
Activity seven point two, Let us measure. Let us now use a digital clinical thermometer to measure body temperature. You may measure your own temperature as well as the temperature of some of your friends. Talk to your friends to find out who would be willing to get their body temperatures measured by you. First, wash your hands and the tip of the digital thermometer with soap and water. Reset the thermometer by pressing the reset button. Place the thermometer under the tongue and close your mouth. Wait till the thermometer makes a beeping sound or flashes a light. Take it out from the mouth and read the temperature on the digital display. Record the temperature in Table seven point one. Clean the tip of the thermometer with soap and water, and dry it. Repeat the above steps for measuring the temperatures of your friends. Here are the precautions to be taken while using a digital clinical thermometer. It is to be used after reading the instruction manual of the thermometer. The tip of the thermometer is to be washed with soap and water before and after use. While washing, care is to be taken to keep the digital portion such as the display out of water. Do not hold the thermometer by the tip. Table seven point one lists the body temperatures of ten persons, with columns for serial number, name, and temperature in degree Celsius.
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The normal temperature of a healthy human body is taken to be thirty seven point zero degree Celsius. But in this activity, did you find that the normal temperature of every person was thirty seven point zero degree Celsius? Or did you find the temperature slightly higher or lower for some people? The temperature of every person may not be thirty seven point zero degree Celsius. What we call normal temperature is the average body temperature of a large number of healthy people. A perfectly healthy person may, therefore, have a normal temperature slightly different from thirty seven point zero degree Celsius. The body temperature is influenced by several factors, such as age, time of the day and activity level. You may try measuring your own temperature at different times of the day and on different days. Record the thermometer readings in your notebook. After a month, analyse your temperature record and see if there are any variations. If yes, try to think what might be the reasons for that. The temperature of human beings does not normally go below thirty five degree Celsius or above forty two degree Celsius. For measuring the body temperature of small children or old people, the digital thermometer can also be placed in the armpit. The temperature measured this way is about zero point five degree Celsius to one degree Celsius lower than the actual body temperature.
There is another scale of temperature known as Fahrenheit scale. On this scale, the unit of temperature is degree Fahrenheit and is denoted by °F. A temperature measured as thirty seven point zero degree Celsius on Celsius scale is equivalent to ninety eight point six degree Fahrenheit 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 is kelvin.
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Let us address some common questions. Do small children generally have slightly higher body temperatures as compared to adults? Do old people, even when healthy, generally have lower body temperatures than young adults? I have seen a friend of mine using a digital thermometer that reads temperature on a different scale. It shows the normal temperature of a healthy human body as ninety eight point six degree Fahrenheit. What is the reason for this difference? The reason is that the thermometer is using the Fahrenheit scale instead of the Celsius scale.
All three temperature scales, Celsius scale, Fahrenheit scale and Kelvin scale are named in honour of the scientists who developed these scales. We can easily convert the temperature from Celsius scale to Kelvin scale by using the formula: Temperature in Kelvin scale equals Temperature in Celsius scale plus two hundred seventy three point one five.
More to know: The names of temperature scales, Celsius scale, Fahrenheit scale and Kelvin scale, start with a capital letter. For the units for temperature, degree 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.
Can a clinical thermometer be used for measuring the temperature of boiling water? Or for measuring the temperature of ice? No, the temperatures of boiling water and ice are outside the range of a clinical thermometer.
Do you know? How was fever detected before thermometers were developed? Fever affects the pulse rate of a person. This was known even in olden days in India. However, apart from fever, some other situations also affect the pulse rate. Hence, pulse rate alone is not a reliable indicator of fever. How can we measure temperatures beyond the range of a clinical thermometer?
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Section seven point three point two, 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 Figure seven point three a. 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, which is coloured red to make it easily seen, or mercury.
Activity seven point three, Let us observe. Let us try to find the temperature range of a given laboratory thermometer. Take a laboratory thermometer and observe it carefully. Note down the following: What is the lowest temperature it can measure? What is the highest temperature it can measure? So, the range of this thermometer is from minus ten degree Celsius to one hundred ten degree Celsius. Precautions to be taken while using a laboratory thermometer: Handle with care. If it hits against some hard object, it can break. Do not hold it by the bulb. Now look at the thermometer shown in Figure seven point three a carefully. Can you tell its range? Its range is from minus ten degree Celsius to one hundred ten degree Celsius.
Activity seven point four, 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 seven point three 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 determined by dividing the difference by the number of divisions. Figure seven point three b shows a closeup of a part of the thermometer shown in Figure seven point three a. Can you now find the smallest value that this thermometer can read? For the thermometer shown in Figure seven point three b, the temperature difference indicated between zero degree Celsius and ten degree Celsius or between ten degree Celsius and twenty degree Celsius is ten degree Celsius. And the number of divisions between these marks are ten divisions. So, one small division can read ten divided by ten equals one degree Celsius. That is, the smallest value that this thermometer can read is one degree Celsius. Your school laboratory may have thermometers for which the range and the value of the smallest division 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 a given laboratory thermometer can read. We will now learn how to measure temperature using a laboratory thermometer. But, let us first learn how to use a laboratory thermometer correctly.
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Correct way of measuring temperature using a laboratory thermometer. In Figure seven point four, we see a laboratory thermometer immersed in warm water inside a beaker. When the thermometer is immersed in water, its bulb should not touch the bottom or the sides of the beaker. The thermometer should be held vertically. It should not be tilted. The temperature must be read while the thermometer is immersed in water. While reading the thermometer, the eye should be directly in line with the level of the liquid column to be read.
Activity seven point five, Let us measure. Take some warm water in a beaker. Dip the thermometer in water so that the bulb is immersed in water, as shown in Figure seven point four. Observe the rise of liquid column in the thermometer. Wait till the column stops rising and note the temperature. Do not wait too long, otherwise, the water itself will start to cool. What is the temperature of water measured by you? Compare it with the readings of your friends. 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. Can we use a laboratory thermometer for measuring body temperature of a person? No, because its range and design are not suitable for body temperature measurement.
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? Laboratory thermometer with crushed ice, and laboratory thermometer with boiling water over a burner. Read the temperatures of ice and boiling water again after some time. Are the temperatures same or have changed? You may have noticed that the temperature of water remains constant while it is boiling. Also, the temperature of ice remains constant while it is melting. Caution: This activity should be performed strictly only under supervision of the teacher. Do not touch the experimental setups.
Activity seven point six, 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 seven point two. Phiban recorded ninety seven point eight degree Celsius, Shemphang recorded ninety eight point zero degree Celsius, Onestar recorded ninety seven point nine degree Celsius, Kloi recorded ninety eight point zero degree Celsius, and Bandarisha recorded ninety eight point one degree Celsius. 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.
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Section seven point three point three, Air temperature. You might have seen thermometers, such as the one shown in Figure seven point five, 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.
Activity seven point seven, Let us analyse. Read or listen to the weather reports for a place for ten successive days. Record the maximum and minimum air temperature for each day in Table seven point three. Analyse the data in Table seven point three. 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 monitored at weather stations all over the world. The data gathered on air temperature along with various other parameters are used for making weather forecasts.
More to know: Know a scientist. Anna Mani, born in nineteen eighteen and passed away in two thousand one, was an Indian scientist, also known as the Weather Woman of India. She invented and built a large number of weather measurement instruments. 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.
Let us review the keywords and summary. The temperature of a body tells us how hot or cold it is. The three most used scales of temperature are the Celsius scale, the Fahrenheit scale, and the Kelvin scale. The units of temperature in these scales are degree Celsius, degree Fahrenheit, and kelvin. 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 thirty seven point zero degree Celsius or ninety eight point six degree Fahrenheit. Laboratory thermometers typically have a temperature range from minus ten degree Celsius to one hundred ten degree Celsius.
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Now, let us enhance our learning by solving the exercises step by step.
Question one: The normal temperature of a healthy human being is close to which option? The correct answer is thirty seven point zero degree Celsius.
Question two: thirty seven degree Celsius is the same temperature as which option? The correct answer is ninety eight point six degree Fahrenheit.
Question three: Fill in the blanks. First blank: The hotness or coldness of a system is determined by its temperature. Second blank: The temperature of ice cold water cannot be measured by a clinical thermometer. Third blank: The unit of temperature is degree Celsius.
Question four: The range of a laboratory thermometer is usually which option? The correct answer is minus ten degree Celsius to one hundred ten degree Celsius.
Question five: Four students used a laboratory thermometer to measure the temperature of water as shown in Figure seven point six. Who do you think followed the correct way for measuring temperature? In Figure seven point six, Student one holds it at an angle, Student two holds it vertically with the bulb immersed and not touching the beaker, Student three touches the bottom, and Student four holds it by the bulb. The correct way is followed by Student two.
Question six: Colour to show the red column on the drawings of thermometers as per the temperatures written below: fourteen degree Celsius, seventeen degree Celsius, and seven point five degree Celsius. In Figure seven point seven, you would colour the liquid column up to the mark indicating fourteen, then up to seventeen, and finally halfway between seven and eight for seven point five.
Question seven: Observe the part of thermometer shown in Figure seven point eight and answer. First, what type of thermometer is it? It is a laboratory thermometer. Second, what is the reading of the thermometer? The liquid column is at twenty six degree Celsius. Third, what is the smallest value that this thermometer can measure? The difference between twenty and thirty is ten degrees, divided into ten small marks, so the smallest value is one degree Celsius.
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Question eight: A laboratory thermometer is not used to measure our body temperature. Give a reason. The reason is that a laboratory thermometer does not have a kink to hold the reading, so the liquid level falls immediately when removed from the body, making it impossible to read accurately. Also, its range is much wider than needed for body temperature.
Question nine: 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 seven point four. First, what was Vaishnavi's highest recorded temperature? Looking at the table, the highest is forty point zero degree Celsius. Second, on which day and at what time was Vaishnavi's highest temperature recorded? It was recorded on Day One at seven pm. Third, on which day did Vaishnavi's temperature return to normal? Normal is thirty seven point zero degree Celsius. On Day Three, at four pm, the temperature was exactly thirty seven point zero degree Celsius, so it returned to normal on Day Three.
Question ten: If you have to measure the temperature twenty two point five degree Celsius, which of the following three thermometers will you use in Figure seven point nine? Explain. You will use thermometer b. Thermometer a has large divisions, thermometer b has finer divisions that allow reading half degrees, and thermometer c has different divisions. To measure twenty two point five degree Celsius accurately, you need a thermometer with a smallest division of zero point five degree Celsius, which is shown in thermometer b.
Question eleven: The temperature shown by the thermometer in Figure seven point ten is which option? The liquid level is exactly halfway between twenty seven and twenty eight, so it is twenty seven point five degree Celsius.
Question twelve: A laboratory thermometer has fifty divisions between zero degree Celsius and one hundred degree Celsius. What does each division of this thermometer measure? The total difference is one hundred degrees. Divided by fifty divisions, each division measures one hundred divided by fifty equals two degree Celsius.
Question thirteen: Draw the scale of a thermometer in which the smallest division reads zero point five degree Celsius. You may draw only the portion between ten degree Celsius and twenty degree Celsius. To draw this, mark ten and twenty as the main marks. Between them, there will be twenty small divisions because the difference is ten degrees, and each small division is zero point five degree Celsius. So, ten divided by zero point five equals twenty divisions.
Question fourteen: Komal tells you that she has a fever of one hundred one degrees. Does she mean it on the Celsius scale or Fahrenheit scale? She means it on the Fahrenheit scale, because one hundred one degree Celsius would be impossible for a human body, whereas one hundred one degree Fahrenheit is a common fever temperature.
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Now, let us move to the Learning Further section. First, 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. You can use a veterinary digital thermometer inserted rectally or placed in the ear, following specific animal safe procedures. Second, if there is any veterinary hospital in your vicinity, you may visit to see the body temperature of animals being measured. Third, find out which places in India are usually regarded to be the coldest and hottest. Dras in Ladakh is often regarded as the coldest, and Phalodi in Rajasthan is often regarded as the hottest. Fourth, find out the minimum and maximum temperatures recorded for these places. Dras can drop to around minus forty five degree Celsius, and Phalodi can reach up to fifty one degree Celsius. Fifth, various planets in our Solar System are at different distances 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. The order is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Does the average temperature of planets decrease as their distance from the Sun increases? Generally yes, but Venus is hotter than Mercury due to its thick greenhouse atmosphere. Sixth, hang a room thermometer in your classroom. Set up the apparatus, as shown in Figure seven point eleven, near the thermometer hung on the wall. Take the readings of thermometers one and two three times during the day, say, first period, lunch break, and last period. Record your readings. Compare the readings and draw your conclusions. Repeat this for two weeks. You will likely find that room temperature and water temperature vary throughout the day, with water temperature changing more slowly than air temperature.
More to know: The temperature at the core of the Sun reaches as high as fifteen million degrees Celsius. Are there objects in the sky that have even higher temperatures? There is no limit on the highest temperature that can exist. However, as per scientific understanding, there is a limit to the lowest temperature that can be achieved. It is close to minus two hundred seventy three point one five degree Celsius, which is zero kelvin, and is called absolute zero.
Thank you for listening! Keep revising and practicing. Goodbye! [CHAPTER_COMPLETE]