Latest Science NCERT Notes and Solutions (Class 6th to 10th)
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Latest Science NCERT Notes and Solutions (Class 11th)
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Latest Science NCERT Notes and Solutions (Class 12th)
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Class 6th Chapters
1. The Wonderful World of Science	2. Diversity in the Living World	3. Mindful Eating: A Path to a Healthy Body
4. Exploring Magnets	5. Measurement of Length and Motion	6. Materials Around Us
7. Temperature and its Measurement	8. A Journey through States of Water	9. Methods of Separation in Everyday Life
10. Living Creatures: Exploring their Characteristics	11. Nature’s Treasures	12. Beyond Earth

Chapter 7: Temperature And Its Measurement

This chapter is about understanding the concept of temperature and how we measure it. It starts with a scenario where a girl checks her brother's temperature using a thermometer, highlighting that while our sense of touch can give an idea, a device is needed for accurate measurement.

As scientist Anna Mani said, "Wrong measurements are worse than no measurements at all." This emphasizes the importance of using reliable methods for measurement.

Hot Or Cold?

We intuitively understand that some things are hotter or colder than others based on our sense of touch. For instance, water from a refrigerator feels colder than tap water.

However, our sense of touch is not always reliable for determining the degree of hotness or coldness. An activity involving dipping hands into warm, cold, and tap water shows that the same tap water can feel cold to a hand that was previously in warm water and warm to a hand that was previously in cold water.

Experiment feeling hot and cold water with different hands

This demonstrates that our perception of hot and cold is relative and can be influenced by our previous experience. Therefore, we need a more dependable way to measure how hot or cold something is.

Temperature

The reliable measure of the degree of hotness or coldness of an object or a substance is called its temperature.

A hotter body has a higher temperature.
A colder body has a lower temperature.

The difference in temperature between two bodies tells us how much hotter one is compared to the other.

A device used to measure temperature accurately is called a thermometer.

Measuring Temperature

There are different types of thermometers designed for measuring different temperature ranges and for different purposes.

Clinical Thermometer

A clinical thermometer is specifically designed to measure human body temperature.

Modern clinical thermometers are often digital and run on batteries. They have a sensor tip and a digital display to show the temperature reading.

Older clinical thermometers used mercury inside a glass tube, but digital thermometers are now preferred because mercury is toxic and digital readings are easier to take and read.

During the COVID-19 pandemic, non-contact or infrared thermometers were widely used. These can measure body temperature from a distance without physical contact, helping to prevent the spread of infections.

Clinical thermometers commonly use the Celsius scale (°C) or the Fahrenheit scale (°F) to measure temperature.

The normal temperature of a healthy human body is generally considered to be 37.0 °C. This corresponds to 98.6 °F on the Fahrenheit scale.

It's important to note that 37.0 °C is an average value for a large number of healthy people. An individual's normal temperature might be slightly different (a little higher or lower) and can vary based on factors like age, time of day, and activity level.

Precautions when using a digital clinical thermometer:

Read the instruction manual before use.
Clean the tip with soap and water before and after measuring.
Avoid getting the digital display part wet.
Do not hold the thermometer by the sensor tip.
Place the tip under the tongue or in the armpit (armpit reading might be slightly lower).
Wait for the signal (beep or light flash) indicating the reading is ready.

Clinical thermometers have a limited range, usually from 35 °C to 42 °C (or 94 °F to 108 °F), which is suitable for the typical range of human body temperature. This means they cannot be used to measure temperatures outside this range, such as the temperature of boiling water or freezing ice.

Extra Information: Before thermometers, fever was sometimes detected by feeling the pulse rate, which is affected by fever, but this is not a reliable indicator alone.

Note on Scales: Temperature scales are named after scientists (Celsius, Fahrenheit, Kelvin). The SI unit of temperature is kelvin (K). The relationship between Celsius and Kelvin is: $ \text{Temperature in K} = \text{Temperature in } °\text{C} + 273.15 $.

Laboratory Thermometer

Laboratory thermometers are used for measuring temperatures of substances in experiments and for other general purposes, excluding human body temperature.

They typically have a larger range than clinical thermometers, commonly from -10 °C to 110 °C.

A laboratory thermometer consists of a long glass tube with a bulb at one end, containing a liquid (often coloured alcohol or mercury). The liquid column rises or falls as the temperature changes, and the reading is taken from the scale marked on the tube.

Before using, it is important to check the range and the smallest division value of the specific laboratory thermometer. For example, a thermometer might have major marks every 10 °C, with 10 smaller divisions between them, meaning each small division represents $10^\circ \text{C} / 10 = 1^\circ \text{C}$. Other thermometers may have smaller divisions.

Precautions when using a laboratory thermometer:

Handle it carefully as it is made of glass and can break easily.
Do not hold it by the bulb.
Ensure the bulb is completely immersed in the substance whose temperature is being measured.
Make sure the bulb does not touch the bottom or sides of the container.

Hold the thermometer vertically, not tilted.
Read the temperature while the thermometer is still immersed in the substance. This is because the liquid level in a laboratory thermometer usually falls as soon as it is taken out, as it is designed to show the temperature of the substance it is in contact with, not retain a maximum reading like a clinical thermometer (which might have a kink).
Read the temperature with your eye level directly in line with the top of the liquid column to avoid parallax error.

Laboratory thermometers are suitable for measuring temperatures like that of boiling water (around 100 °C) or melting ice (around 0 °C).

Caution: Measuring the temperature of boiling water or melting ice should be done under teacher supervision and with caution.

Air Temperature

The temperature of the air around us is often referred to as air temperature or room temperature.

Room thermometers, like those hung on walls, give an approximate air temperature.

Weather reports commonly mention the maximum and minimum air temperatures recorded during the day. These temperatures vary daily due to changing weather conditions and also show seasonal variations (higher in summer, lower in winter).

Air temperature is a key parameter monitored by weather stations worldwide for making weather forecasts.

Extra Information: Anna Mani, known as the 'Weather Woman of India', made significant contributions by developing various weather measurement instruments, which helped India become more self-reliant in meteorological studies and also explored renewable energy possibilities.

Let us enhance our learning

Question 1. The normal temperature of a healthy human being is close to ________.

(i) $98.6 \text{ °C}$

(ii) $37.0 \text{ °C}$

(iii) $32.0 \text{ °C}$

(iv) $27.0 \text{ °C}$

Answer:

Question 2. $37 \text{ °C}$ is the same temperature as ________.

(i) $97.4 \text{ °F}$

(ii) $97.6 \text{ °F}$

(iii) $98.4 \text{ °F}$

(iv) $98.6 \text{ °F}$

Answer:

Question 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 _________.

Answer:

Question 4. The range of a laboratory thermometer is usually .

(i) $10 \text{ °C}$ to $100 \text{ °C}$

(ii) $-10 \text{ °C}$ to $110 \text{ °C}$

(iii) $32 \text{ °C}$ to $45 \text{ °C}$

(iv) $35 \text{ °C}$ to $42 \text{ °C}$

Answer:

Question 5. Four students used a laboratory thermometer to measure the temperature of water as shown in Fig. 7.6:

Four diagrams showing different ways students are holding a laboratory thermometer to measure water temperature. Each student is labeled 'Student 1', 'Student 2', 'Student 3', 'Student 4'.

Who do you think followed the correct way for measuring temperature?

(i) Student 1

(ii) Student 2

(iii) Student 3

(iv) Student 4

Answer:

Question 6. Colour to show the red column on the drawings of thermometers (Fig. 7.7) as per the temperatures written below:

Three diagrams of thermometers. Below each thermometer, a temperature is indicated: 14 °C, 17 °C, 7.5 °C. The task is to color the mercury column to represent these temperatures.

Answer:

Question 7. Observe the part of thermometer shown in Fig. 7.8 and answer the following questions:

A close-up diagram of a thermometer scale with a mercury column. The scale shows markings from, for example, 35 to 42 degrees Celsius, with the mercury indicating a specific temperature.

(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?

Answer:

Question 8. A laboratory thermometer is not used to measure our body temperature. Give a reason.

Answer:

Question 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
DAY	7am	10am	1pm	4pm	7pm	10pm
One	$38.0 \text{ °C}$	$37.8 \text{ °C}$	$38.0 \text{ °C}$	$38.0 \text{ °C}$	$40.0 \text{ °C}$	$39.0 \text{ °C}$
Two	$38.6 \text{ °C}$	$38.8 \text{ °C}$	$39.0 \text{ °C}$	$39.0 \text{ °C}$	$39.0 \text{ °C}$	$38.0 \text{ °C}$
Three	$37.6 \text{ °C}$	$37.4 \text{ °C}$	$37.2 \text{ °C}$	$37.0 \text{ °C}$	$36.8 \text{ °C}$	$36.6 \text{ °C}$

(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?

Answer:

Question 10. If you have to measure the temperature $22.5 \text{ °C}$, which of the following three thermometers will you use (Fig. 7.9)? Explain.

Three different thermometers labeled (a), (b), and (c) with varying scales and ranges.

Answer:

Question 11. The temperature shown by the thermometer in Fig. 7.10 is

A diagram of a thermometer showing a specific temperature reading.

(i) $28.0 \text{ °C}$

(ii) $27.5 \text{ °C}$

(iii) $26.5 \text{ °C}$

(iv) $25.3 \text{ °C}$

Answer:

Question 12. A laboratory thermometer has 50 divisions between $0 \text{ °C}$ and $100 \text{ °C}$. What does each division of this thermometer measure?

Answer:

Question 13. Draw the scale of a thermometer in which the smallest division reads $0.5 \text{ °C}$. You may draw only the portion between $10 \text{ °C}$ and $20 \text{ °C}$.

Answer:

Question 14. Someone tells you that she has a fever of 101 degrees. Does she mean it on the Celsius scale or Fahrenheit scale?

Answer: