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CuriosityCh 7 Temperature and its Measurement

Temperature and its Measurement: Class 6 Science · Chapter 7

Curiosity · Companion notes, simulations and practice · Official NCERT chapter PDF ↗

Published · Updated

  • 85 min
  • 2 simulations
  • 18 practice questions
  • 17 MCQs

What you will learn in Temperature and its Measurement

  • Explain why the sense of touch cannot reliably tell how hot or cold something is
  • Describe temperature as a measure of hotness and compare things by their temperatures
  • Use a digital clinical thermometer safely and hygienically to measure body temperature
  • Relate the Celsius, Fahrenheit and Kelvin scales and change Celsius temperatures to kelvin
  • Find the range and the value of one division of a laboratory thermometer and read it correctly
  • Follow the correct method and precautions for measuring the temperature of a liquid
  • Record and analyse daily maximum and minimum air temperatures

Original companion text aligned to NCERT Science Class 6, Chapter 7, pp. 123–142. Not affiliated with or endorsed by NCERT.

7.1 Hot or Cold?

It is a sticky afternoon in Jaipur. Your little cousin Chintu bursts in from a cricket match in the lane, red-cheeked and sweaty. Nani has just finished making rotis on the hot tawa. She presses the back of her warm hand to his forehead. “He feels fine,” she says.

Then Mama walks in, holding a chilled bottle of water from the fridge. He touches the same forehead with his cold fingers. “He is burning up!” Two careful grown-ups, one forehead, two opposite answers. Whom should we believe?

We sort things into hot and cold all day long. A steel tumbler of milk fresh off the stove makes you snatch your hand back. A bite of kulfi makes your teeth tingle. For big differences like these, your skin gets it right every time. Small differences are trickier, and your skin can even be tricked. The next activity shows how.

3/3A thermometer in the same bowl gives one answer: 27 °C.

Fig. 7.1Two hands, one bowl, two opposite answers. A thermometer gives just one.NCERT Fig. 7.1 · p. 124

Three steel bowls stand on a table, labelled warm, tap and icy; the warm bowl has steam above it and the icy bowl has floating ice cubes. In the first step hand 1 dips into the warm bowl and hand 2 into the icy bowl, while a clock shows one minute. In the second step both hands are in the tap-water bowl, with a speech bubble for hand 1 saying feels cool and one for hand 2 saying feels warm. In the last step the hands lift out and a digital thermometer standing in the tap water reads 27 °C.

So touch can fool us. Your hands were not lying; they were comparing. That is exactly what happened to Chintu. Nani’s hand was warm from the tawa, so his forehead felt ordinary to her. Mama’s hand was cold from the bottle, so the same forehead felt burning hot to him.

Quick check
1 of 3
Ravi holds a glass of iced lassi for a minute. Then he touches a steel spoon lying on the table. How will the spoon probably feel to him?
Show answer

Answer (A) Warmer than it really is

His chilled fingers compare the spoon with the icy glass, so the spoon feels warmer than it is. It cannot feel colder, because his fingers are now colder than the spoon.

7.2 Temperature

So we need a judge that cannot be tricked. That judge is a thermometer (तापमापी). Its name joins two Greek words: thermo, heat, and meter, measure. Instead of saying “warm-ish” or “very cold”, a thermometer gives a number, and that number is called the temperature (ताप). Your two hands could argue, but a number cannot.

Definition
Temperature

A measure of how hot or cold something is: the hotter it is, the bigger the number.

ExampleBoiling water is at about 100 °C; nimbu pani from the fridge may be at 8 °C.

Temperature puts hotness on a ladder: the hotter the thing, the higher its number. Fig. 7.2 places some everyday things on one scale. Numbers also make comparing easy. Suppose your chai is at 70 °C and your body is at 37 °C. Subtract: 70 − 37 = 33. The chai is 33 °C hotter than you, which is why a big gulp makes you gasp!

4/4Chai at 70 °C is 33 °C hotter than your body at 37 °C.

Fig. 7.2Everything gets a place on one scale. Higher up means hotter. (The values are typical ones.)

A tall thermometer-shaped scale runs from −20 at the bottom to 100 at the top, shaded blue at the cold end and orange at the hot end, beside an arrow labelled hotter. In the first step two rows appear near the bottom: freezer at −18 °C and melting ice at 0 °C. In the second step a room in spring at 25 °C and your body at 37 °C are added. In the third step a cup of hot chai at 70 °C and boiling water at 100 °C appear near the top. In the last step a double arrow joins the chai and the body with the words 33 °C hotter than you.

Thermometers come in many kinds, and two of them star in this chapter. The one in a science lab, the laboratory thermometer, can dip into pond water, a cup of ice or boiling water. The one in your medicine box, the clinical thermometer, has just one job: checking the temperature of a human body.

Definition
Thermometer

An instrument for measuring temperature.

ExampleThe digital thermometer in your family’s medicine box.

SimulationWarm water, busy particles

A closed container of water drawn as moving particles, with a thermometer beside it and readings for temperature, state and the average speed of the molecules. A slider sets the temperature between 5 °C and 90 °C. When the water is cool the particles move slowly and the average speed is lower; as you warm it they move faster and the average speed rises, while the water stays a liquid.

Fig. 7.3Slide the temperature and watch the particles and the Average speed reading.
Try this
  • Set the slider to 10 °C, then to 80 °C. Which way does the Average speed reading change?
  • Is the water still a liquid at both temperatures? Check the State reading.
Quick check
1 of 3
Put these in order, from coldest to hottest.
  1. A healthy child (37 °C)
  2. Ice cream in a freezer (−15 °C)
  3. A glass of tap water (24 °C)
  4. Tea fresh from the kettle (85 °C)
Show answer
Answer
  1. Ice cream in a freezer (−15 °C)
  2. A glass of tap water (24 °C)
  3. A healthy child (37 °C)
  4. Tea fresh from the kettle (85 °C)
Temperatures sort things fairly: the lower the number, the colder the thing. A number below zero, like −15 °C, is colder than 0 °C.

7.3 Measuring Temperature

Different jobs need different thermometers. A doctor needs one that is safe to put in your mouth. A science lab needs one that can go into boiling water. A weather station needs one that sits out in the air day and night. Let us meet them one by one.

7.3.1 Clinical thermometer

Open the medicine box at home and you will probably find a slim plastic stick with a metal tip and a little screen. A tiny sensor hidden in the tip feels the warmth of whatever touches it, and a battery no bigger than a shirt button powers the screen. The word clinical comes from clinic, the place where doctors look after patients. And because this thermometer shows its answer in digits, like a calculator, it is called a digital clinical thermometer.

4/4The beep means the reading has stopped changing: 36.8 °C.

Fig. 7.4Using a digital clinical thermometer, one step at a time.NCERT Fig. 7.2 · p. 125

A child’s head in profile, wearing a cap, faces a long white digital thermometer. In the first step labels point to the metal tip, the display and the button. In the second step a ring around the button shows it being pressed and the display reads Lo °C. In the third step the thermometer slides so its tip goes between the child’s lips, and the display reads 35.8 °C with the words tip under the tongue. In the last step curved sound lines and the word beep appear, and the display shows 36.8 °C.

Look at the screen: the reading ends in °C. The little circle stands for degree, and the C stands for the Celsius scale, the scale that clinical thermometers in India are usually set to. So 37 °C is read aloud as “thirty-seven degrees Celsius”.

Doctors call 37.0 °C the normal body temperature. It is not a rule that every body must obey. It is an average. Measure thousands of healthy people and add up all their readings. Divide by the number of people, and the answer comes out very close to 37 °C.

So a healthy you might read 36.7 °C before breakfast and 37.2 °C after a game of kho-kho. A sleepy morning, a busy afternoon, even how old you are: each of these nudges the number a little. Fig. 7.5 shows eight healthy classmates.

3/3A friend with a fever reads 38.6 °C, far from the healthy group.

Fig. 7.5Healthy bodies are not all at exactly 37.0 °C; they cluster around it.

A number line runs from 36.0 to 39.0 °C with small ticks every tenth of a degree. In the first step eight blue dots sit between 36.6 and 37.4, with two dots stacked at 37.0, under the title 8 healthy classmates. In the second step a dashed line marks the average at 37.0 °C and a bracket spans the healthy spread. In the last step an orange triangle at 38.6 °C, labelled a friend with fever, sits well to the right of the group.

Example

The class average

The eight healthy classmates in Fig. 7.5 read 36.6, 36.8, 36.9, 37.0, 37.0, 37.1, 37.2 and 37.4 (all in °C). Find their average temperature.

Try it yourself first. Then reveal the solution one step at a time.

A human body, even a sick one, almost always stays somewhere between about 35 °C and 42 °C. So a clinical thermometer only needs a small window of numbers. In return, it can show tenths of a degree, such as 36.8 °C or 36.9 °C.

A toddler will not keep a thermometer under the tongue, and some grandparents find it hard too. For them, tuck the tip snugly into the armpit. The armpit is a little cooler than the inside of the mouth. So the screen shows less than the true body temperature, by roughly half a degree to one degree.

Other temperature scales

In Dadaji’s old medicine box you find a thermometer that reads 98.6 when he is perfectly well. Is Dadaji boiling? Not at all! This thermometer counts on another scale, the Fahrenheit scale, and its readings end in °F, short for degrees Fahrenheit. On it, a healthy body shows 98.6 °F. That is exactly the same hotness as 37.0 °C, just written in a different “language”. Scientists today rarely use °F, but you will still see it on some fever thermometers and in weather reports from the USA.

Scientists have a favourite scale of their own. It begins at the coldest temperature there can ever be, absolute zero, so it never needs negative numbers. This is the Kelvin scale, and its unit is the kelvin (symbol K). The kelvin is the SI unit of temperature: scientists all over the world have agreed to use it. A step of one kelvin is the same size as a step of one degree Celsius. So changing from Celsius to kelvin needs just one addition:

Celsius to kelvin
temperature in kelvin=temperature in degrees Celsius+273.15

4/4The coldest possible: −273.15 °C = −459.67 °F = 0 K.

Fig. 7.6Three scales, one hotness: each row is one temperature written three ways.

Three upright scales stand side by side, headed Celsius (°C), Fahrenheit (°F) and Kelvin (K), each with a break near the bottom. In the first step a row labelled ice melts shows 0 °C, 32 °F and 273.15 K. In the second step a row labelled healthy body adds 37 °C, 98.6 °F and 310.15 K. In the third step a row labelled water boils adds 100 °C, 212 °F and 373.15 K. In the last step, below the break, a row labelled absolute zero, coldest possible, shows −273.15 °C, −459.67 °F and 0 K.

Example

From °C to kelvin

A June afternoon in Delhi reaches 44 °C. A freezer keeps ice cream at −18 °C. Write both temperatures in kelvin.

Try it yourself first. Then reveal the solution one step at a time.

Compare

Spot the difference

Write it like this

  • 37 °C
  • 310 K
  • 40 degrees Celsius
  • the Celsius scale
  • 25 °C in the shade

Not like this

  • 37°C, or 37 °c
  • 310 °K
  • 40 degree celsius
  • the celsius scale
  • 25 °C. in the shade
Quick check
1 of 4
Leela’s healthy grandmother gets an armpit reading of 36.3 °C. Her true body temperature is most likely about:
Show answer

Answer (C) 37.0 °C

An armpit reading falls short of the true value by roughly half a degree to one degree. So 36.3 °C points to roughly 36.8 °C to 37.3 °C, which is about 37.0 °C.

A clinical thermometer is no help in checking whether the dal is boiling or the ice tray has frozen. Those temperatures lie far outside its narrow window, and very hot food could even damage it. For jobs like these we need a different tool.

7.3.2 Laboratory thermometer

A laboratory thermometer is a lift for a liquid. Warm a liquid and it expands, so it needs more room; cool it and it shrinks back. The thermometer turns that tiny change into a movement you can see.

Follow the liquid on its trip. It starts in a round bulb at the bottom. Warm the bulb and the liquid swells. Its only way out is a hair-thin channel, the bore, running up a sealed glass tube. The bore is so narrow that even a tiny swelling pushes the thread a long way up. Cool the bulb and the thread slides back down. Beside the bore runs a scale of degree marks: the mark level with the tip of the thread is the temperature.

2/3In warm water the liquid expands: the column rises to 45 °C.

Fig. 7.7Warm the bulb and the column rises; cool it and the column falls.NCERT Fig. 7.3a · p. 130

An upright laboratory thermometer with a scale from below 0 to above 100 °C and labels pointing to the sealed glass tube, the narrow bore, the scale marks and the bulb of liquid. In the first step the red column stops at 25 °C, labelled reads 25 °C. In the second step the bulb sits in a beaker of steaming warm water and the column rises to 45 °C. In the last step the bulb sits in icy water with ice cubes and the column falls to 2 °C.

Definition
Value of one division

The temperature change shown by one small space on a thermometer’s scale: the smallest change it can show.

ExampleNumbered marks 10 °C apart with 10 spaces between them: each division is 1 °C.

4/4The column ends 7 divisions past 30: 30 + 7 × 0.5 = 33.5 °C.

Fig. 7.8Difference between two numbered marks ÷ number of spaces = value of one division.NCERT Fig. 7.3b · p. 131

A long horizontal close-up of a thermometer scale with numbered marks at 30 and 35, small marks between them and a red liquid column along the bottom. In the first step the marks 30 and 35 are circled and the words 35 − 30 = 5 °C appear. In the second step the ten spaces between them are shaded one after another and numbered 1 to 10. In the third step a box shows 5 °C ÷ 10 = 0.5 °C. In the last step a green bar marks the column from 30 to its top, and the words 30 + 7 × 0.5 = 33.5 °C appear.

Example

Read a coarse thermometer

On Aarav’s thermometer the numbered marks go 0, 20, 40, 60 and so on. Between 40 and 60 there are 10 small spaces. The liquid ends 3 small divisions above the 40 mark. (a) What is one division worth? (b) What does the thermometer read?

Try it yourself first. Then reveal the solution one step at a time.

InteractiveThermometer reading lab

An interactive thermometer trainer. On the left is a whole thermometer with its range; an orange frame on it shows which part is magnified on the right, where the small divisions and numbered marks are large and easy to count. In Read it mode you pick what one small division is worth from five buttons, then type the temperature shown; a hint appears after a wrong try and the answer is explained after a second one. In Set it mode you drag the red column or use arrow buttons to show a given temperature, then check it. A button switches between thermometers with 1 °C, 0.5 °C and 2 °C divisions, including one that reads below zero.

Fig. 7.9Practise on four different thermometers. In Read it, find what one division is worth, then type the reading. In Set it, drag the red column (or use the arrows) to show the temperature asked for. Aim for five right first time!

Even a good thermometer gives a wrong answer if it is used carelessly. Before you trust a reading of a liquid, make SURE:

  • Straight: the thermometer stands upright, not slanting.
  • Under: the whole bulb is under the liquid, in the middle, touching neither the bottom nor the sides.
  • Read in place: you read it while the bulb is still in the liquid.
  • Eye level: your eye is level with the top of the liquid thread.

4/4✓ Upright, bulb in the middle of the water, eye level with the column.

Fig. 7.10Three common slips, then the right way.NCERT Fig. 7.4 · p. 132

A beaker of steaming warm water and a laboratory thermometer, with a cross or tick badge at the top. In the first step the bulb rests on the bottom of the beaker, circled, with the words bulb touches the bottom. In the second step the thermometer leans at a slant beside a dashed upright line, with the words thermometer is tilted. In the third step the thermometer stands outside the beaker with a downward arrow labelled falling, and the words read after taking it out. In the last step, marked with a tick, the thermometer stands upright with its bulb in the middle of the water, and a dashed line joins the top of the column to an eye at the same height.

Why does the height of your eye matter? The scale is marked on the front of the glass, while the liquid thread sits a little way inside. If you look from above or below, your line of sight crosses the scale at the wrong mark, as Fig. 7.11 shows.

3/3Eye level with the column: 40 °C, the true reading.

Fig. 7.11Where your eye is decides where your sight line crosses the scale. (Drawn much bigger than real life.)

A magnified side view of a thermometer: a thick slice of glass with the liquid thread inside, its top at 40, and scale marks on the front surface numbered from 36 to 44. In the first step an eye sits high on the right and a dashed sight line from the eye to the top of the liquid crosses the scale at 41: reads 41 °C, too high. In the second step the eye sits low and the line crosses the scale at 39: reads 39 °C, too low. In the last step the eye is level with the top of the liquid and the line crosses at 40: reads 40 °C, correct.

SimulationHeat ice all the way to vapour

A closed container of water drawn as particles, with a thermometer and readings for temperature, state and particle speed. It starts as ice at −10 °C. A slider sets the heater’s target temperature from −20 °C to 120 °C. As the water heats, the temperature climbs to 0 °C and waits there while the ice melts, then climbs to 100 °C and waits there while the water boils into vapour, before rising again.

Fig. 7.12Set a high temperature and keep an eye on the Temperature reading. Where does it pause? (The sim calls hot water vapour “steam”.)
Try this
  • Start at −10 °C and drag the slider to 20 °C. What does the Temperature reading show while the State says Melting?
  • Now drag the slider to 110 °C. At what temperature does the reading wait while the water is boiling?
ExampleNCERT Activity 7.6 · p. 133

How close are the readings?

Leave out Karthik’s odd reading. Using the other five readings of the boiling water, find (a) the highest and lowest readings and (b) the difference between them.

Try it yourself first. Then reveal the solution one step at a time.

Quick check
1 of 4
On a thermometer, the numbered marks 50 °C and 60 °C have 20 small spaces between them. What is one small division worth?
°C
Show answer

Answer 0.5 °C

60 − 50 = 10 °C, and 10 ÷ 20 = 0.5 °C for each division.

7.3.3 Air temperature

How warm is your classroom right now? To find out, you need a thermometer that simply hangs in the air: a room thermometer. Most are a liquid thermometer fixed to a small board, with a scale from below 0 °C to about 50 °C. Hang one on an inside wall, away from sunny windows, lamps and fans. It then tells you roughly how warm the air in the room is. Some homes have digital ones that show the room temperature beside a clock.

Open the weather page of a newspaper, or a weather app, and look up your town. For each day you will find two air temperatures. One is the maximum, the highest of the day. The other is the minimum, the lowest. The maximum usually comes in the afternoon, and the minimum early in the morning, around sunrise.

Definition
Air temperature

How hot or cold the air is at a place. Weather reports give each day’s highest (maximum) and lowest (minimum) air temperature.

4/4Both lines creep upward as summer comes.

Fig. 7.13A sample ten-day record for Bhopal, 20 to 29 March. The numbers wobble, but both lines slowly climb.

A line chart with the dates 20 to 29 March along the bottom and temperature from 15 to 40 °C up the side. In the first step an orange solid line with dots shows each day’s maximum, starting at 33 °C, dipping to 32 °C on the 24th and climbing to 39 °C on the 29th. In the second step a blue dashed line with squares shows the minimum, rising from 18 °C to 23 °C. In the third step a double arrow on 20 March spans the 15 °C gap between maximum and minimum. In the last step a thick arrow between the two lines slopes upward, labelled getting warmer.

Why do the lines wobble? The air takes its cue from the day’s weather: a cloudy sky, a cool breeze or a shower can all hold the temperature down. Look at 24 March in the chart, when clouds kept the maximum low. Step back and look at several weeks, and a slower pattern appears. The lines creep up as the hot months near, and slide down again when the cold months come.

ExampleNCERT Activity 7.7 · p. 134

Reading a weather table

Here is a five-day record for Darjeeling in December. (a) Which day had the coldest early morning? (b) Which day had the biggest gap between maximum and minimum?

Table 7.10Darjeeling in December
DayMaximum (°C)Minimum (°C)
Monday124
Tuesday115
Wednesday133
Thursday102
Friday124

Try it yourself first. Then reveal the solution one step at a time.

To measure air temperature properly, a thermometer must stay out of the sunshine, or it would measure the Sun warming its own glass. Weather stations keep their thermometers in a white box with slatted sides, raised above the ground in the open. Air flows in through the slats, but direct sunlight cannot. Every day, readings from thousands of these boxes, together with rainfall, wind and humidity, flow to weather scientists. That is how tomorrow’s forecast gets made.

Quick check
1 of 3
At what time of day is the minimum air temperature usually reached?
Show answer

Answer (B) Early in the morning, around sunrise

The ground and air lose warmth all night, so the lowest temperature usually comes around sunrise. The maximum comes in the afternoon.
Flash cards · 12

Words to remember

1 / 12
Recap

Temperature and its Measurement: key points and summary

  1. Touch compares; it does not measure. The same water can feel cool to one hand and warm to the other (Section 7.1).
  2. Temperature tells how hot or cold something is: the higher the temperature, the hotter it is (Section 7.2).
  3. A thermometer measures temperature. Clinical thermometers are for our bodies; laboratory thermometers are for most other things (Section 7.2).
  4. A digital clinical thermometer shows body temperature in °C on a screen. Clean its tip before and after every use (Section 7.3.1).
  5. Normal body temperature, 37.0 °C or 98.6 °F, is an average. Healthy people differ a little from it (Section 7.3.1).
  6. The three common scales are Celsius (°C), Fahrenheit (°F) and Kelvin (K). The kelvin is the SI unit, and kelvin = degrees Celsius + 273.15 (Other temperature scales).
  7. A laboratory thermometer has a bulb of liquid and a narrow bore. A typical one reads from −10 °C to 110 °C (Section 7.3.2).
  8. One small division = difference between two numbered marks ÷ number of spaces between them (Section 7.3.2).
  9. Measure a liquid with the thermometer upright, the bulb in the liquid and clear of the container, and your eye level with the column (Section 7.3.2).
  10. While ice melts or water boils, the temperature stays steady (Section 7.3.2).
  11. Weather reports give each day’s maximum and minimum air temperature, and these change from day to day (Section 7.3.3).
Fig. 7.14Close-ups P, Q and R for the exercises. All scales are in °C.NCERT Fig. 7.8 · p. 138

Three horizontal close-ups of thermometer scales, one above the other, all in degrees Celsius. P has numbered marks at 10, 20, 30 and 40 with 5 small spaces between neighbouring marks, and its red column ends 3 small divisions past the 20 mark. Q has numbered marks at −10, −5, 0, 5 and 10 with 5 small spaces between neighbouring marks, and its column ends 4 small divisions below the 0 mark. R has numbered marks at 16, 18, 20, 22 and 24 with 4 small spaces between neighbouring marks and a slightly longer mark halfway between them; its column ends 3 small divisions past the 20 mark.

Table 7.11Dadi’s hospital temperature chart (°C)NCERT Table 7.4 · p. 139
Day6 am6 pm
Monday38.439.2
Tuesday38.939.4
Wednesday38.338.7
Thursday37.637.9
Friday37.037.2
Practice · 18 questions

Practice questions with answers (NCERT “Exercises”)

  1. Quick answerEasyNCERT Exercises Q1

    After a week of good food and sleep, Ishita is fit again. Which reading would you now expect from her clinical thermometer?

    Show answer

    Answer (D) 37.0 °C

    Healthy people read close to 37.0 °C. The number 98.6 belongs with °F, not °C; 35.0 °F is colder than ice; and 40.5 °C would be a high fever.
  2. Quick answerEasyNCERT Exercises Q2

    A thermometer marked in °F shows 98.6 °F. The same temperature on the Celsius scale is:

    Show answer

    Answer (D) 37.0 °C

    98.6 °F and 37.0 °C describe the same healthy body temperature on two different scales. Keeping the number 98.6 but writing °C would mean a body hotter than a cup of chai, and 310.15 is the kelvin value, which is never written with °C.
  3. Quick answerEasyNCERT Exercises Q3

    Fill in the blanks. (i) The SI unit of temperature, used by scientists everywhere, is the . (ii) Kavya’s thermometer shows 36.9 °C, and the °C means degrees . (iii) Your fingers can be fooled, but a thermometer tells you the exact of a cup of tea. (iv) You cannot check a pot of boiling dal with a thermometer, because it only reads from about 35 °C to 42 °C.

    Show answer

    Answer (1) kelvin, (2) Celsius, (3) temperature, (4) clinical

    The kelvin (K) is the SI unit; °C means degrees Celsius; a thermometer measures temperature; and a clinical thermometer has only a small range around body temperature.
  4. Quick answerEasyNCERT Exercises Q4

    Match each thermometer with the range it usually has.

    Tap an item on the left, then its match on the right.

    Show answer
    Answer
    • Digital clinical thermometer : about 35 °C to 42 °C
    • School laboratory thermometer : about −10 °C to 110 °C
    • Room thermometer on a wall : about −10 °C to 50 °C
    A clinical thermometer only needs body temperatures. A laboratory thermometer must handle ice and boiling water. A room thermometer only needs the temperatures that air in a room can reach.
  5. Short answerMediumNCERT Exercises Q5

    Kabir has to find the temperature of some warm water in a beaker. Here is exactly what he does. Step 1: He grips the thermometer near the bulb so that it will not slip. Step 2: He lowers it until the bulb rests on the bottom of the beaker. Step 3: He keeps it upright and waits until the column stops rising. Step 4: He lifts it out and carries it to the window, where the light is better, to read it.

    1. Which of Kabir’s steps are mistakes? Pick all of them.

      Select all that apply
      Show answer
      Answer
      • (A) Step 1
      • (B) Step 2
      • (D) Step 4
      Steps 1, 2 and 4 are mistakes. Only Step 3 is right: the thermometer should be upright, and you wait until the column stops rising.

    2. Rewrite his method so that every step is right.

      Show solution

      AnswerHold it near the top, let the bulb hang in the middle of the water, keep it upright until the column stops, and read it in the water with your eye level with the column.

      Step 1: fingers on the bulb warm the liquid inside, so he should hold the thermometer near the top. Step 2: a bulb resting on the bottom partly measures the glass instead of the water, so the bulb should hang in the middle of the water. Step 3 was right. Step 4: out of the water the column starts to fall at once, so he should read it with the bulb still in the water, bending down until his eye is level with the top of the column.

  6. DiagramMediumNCERT Exercises Q6

    A coarse laboratory thermometer has a numbered mark every 10 °C, with only 5 small spaces between neighbouring marks. Work out where the top of the red column must be for each temperature. For more practice like this, try Set it in the thermometer reading lab.

    1. For 38 °C, how many small divisions above the 30 °C mark?

      Show answer

      Answer 4

      Each division is 10 ÷ 5 = 2 °C. 38 − 30 = 8 °C, and 8 ÷ 2 = 4, so 4 divisions above the 30 mark.

    2. For 12 °C, how many small divisions above the 10 °C mark?

      Show answer

      Answer 1

      12 − 10 = 2 °C, which is just 1 division of 2 °C above the 10 mark.

    3. Where does the top of the column go for 25 °C?

      Show solution

      AnswerHalfway between the 2nd and 3rd small marks above the 20 °C mark.

      Each division is 2 °C, so the 2nd small mark above 20 stands for 24 °C and the 3rd for 26 °C. 25 °C lies halfway between them, so the column ends in the middle of that space.

  7. Short answerMediumNCERT Exercises Q7

    Close-up Q in Fig. 7.14 comes from a thermometer standing in a bowl of ice mixed with salt.

    1. What is one small division on Q worth?

      °C
      Show answer

      Answer 1 °C

      Numbered marks 5 °C apart with 5 spaces between them: 5 ÷ 5 = 1 °C.

    2. What temperature does Q show?

      °C
      Show answer

      Answer -4 °C

      The column ends 4 divisions below the 0 mark (1 division above the −5 mark), so it reads 0 − 4 × 1 = −4 °C.

    3. The ice melts and the mixture warms up by 9 °C. What will Q read then?

      °C
      Show answer

      Answer 5 °C

      −4 + 9 = 5 °C: the column now ends 5 divisions above the 0 mark.

    4. Could Q be part of a clinical thermometer? Give a reason.

      Show solution

      AnswerNo. Its marks go below 0 °C, far outside the 35 °C to 42 °C of a clinical thermometer.

      No. A clinical thermometer only needs about 35 °C to 42 °C. Q has marks from −10 °C upward, so it belongs to a laboratory or room thermometer.

  8. Short answerMediumNCERT Exercises Q8

    Your cousin wants to use the school’s laboratory thermometer to check her fever. Give two reasons why this is not a good idea.

    Show solution

    AnswerIts reading starts falling as soon as it leaves the mouth, and a long glass tube is unsafe in the mouth. Its 1 °C divisions are also too coarse for a fever.

    A laboratory thermometer must be read while its bulb still touches what it measures. Once it leaves the mouth, its column starts falling, so the reading comes out too low. Its divisions are usually 1 °C, too coarse to tell 37.4 °C from 37.8 °C. It is also a long glass tube that breaks easily, and some contain poisonous mercury. A clinical thermometer is built for this job.

  9. Short answerMediumNCERT Exercises Q9

    After an infection, Dadi spent five days in hospital. A nurse wrote down her temperature twice a day, at 6 am and at 6 pm (Table 7.11).

    1. When was Dadi’s temperature highest?

      Show answer

      Answer (D) Tuesday at 6 pm

      The biggest number in the chart, 39.4 °C, is in the Tuesday row under 6 pm. Monday at 6 pm (39.2 °C) comes close, but it is a little lower.

    2. How many of the ten readings were above 38 °C?

      Show answer

      Answer 6

      Both readings on Monday, Tuesday and Wednesday are above 38 °C: that makes 6. Thursday and Friday stay below 38 °C.

    3. Dadi’s doctor sends a patient home after a whole day on which every reading stays below 37.5 °C. On which day did Dadi reach that?

      Show answer

      Answer (C) Friday

      Friday’s readings, 37.0 °C and 37.2 °C, are both below 37.5 °C. Thursday is tempting, but 37.6 °C and 37.9 °C are still above 37.5 °C.

    4. By how much did her temperature fall from the highest reading to the very last one?

      °C
      Show answer

      Answer 2.2 °C

      The highest reading is 39.4 °C and the last one is 37.2 °C: 39.4 − 37.2 = 2.2 °C.
  10. Short answerMediumNCERT Exercises Q10

    Compare the three close-ups in Fig. 7.14. Each one is part of a longer thermometer whose small divisions carry on in the same way beyond the part you can see.

    1. Which one could not show 27 °C exactly on a mark?

      Show answer

      Answer (A) P

      P’s divisions are 2 °C, so it has marks for 26 °C and 28 °C but nothing in between: 27 °C falls between two marks. Q’s divisions are 1 °C and R’s are 0.5 °C, so both have a mark at 27 °C.

    2. Only one of them could show 18.5 °C exactly. Which one, and why?

      Show solution

      AnswerR, because only R has a mark for every half degree.

      P’s divisions are 2 °C and Q’s are 1 °C, so neither has a mark at 18.5 °C. R has 4 spaces between marks 2 °C apart, so each division is 0.5 °C, and 18.5 °C is the first small mark after 18.

  11. Short answerMediumNCERT Exercises Q11

    Read the close-ups P and R in Fig. 7.14.

    1. What temperature does P show?

      °C
      Show answer

      Answer 26 °C

      P has 5 spaces between marks 10 °C apart, so one division is 2 °C. The column ends 3 divisions past 20: 20 + 3 × 2 = 26 °C.

    2. What temperature does R show?

      Show answer

      Answer (C) 21.5 °C

      R has 4 spaces between marks 2 °C apart, so one division is 2 ÷ 4 = 0.5 °C. The column ends 3 divisions past 20: 20 + 3 × 0.5 = 21.5 °C. Dividing by the 5 lines instead of the 4 spaces would give 21.2 °C, and taking each division as 1 °C would give 23.0 °C.
  12. NumericalMediumNCERT Exercises Q12

    A thermometer maker wants each small division to stand for 0.5 °C. How many equal divisions must she mark between the 0 °C and 40 °C marks?

    Show solution

    The marks are 40 − 0 = 40 °C apart. Each division is 0.5 °C, so she needs 40 ÷ 0.5 = 80 divisions. Check: 80 × 0.5 = 40 °C.

  13. DiagramHardNCERT Exercises Q13

    Design a close-up scale for a fever thermometer: numbered marks at 36, 37 and 38 °C, with each small division worth 0.2 °C. Show where the column would end for a reading of 37.4 °C.

    1. How many small spaces will there be between the 36 °C and 38 °C marks?

      Show answer

      Answer 10

      38 − 36 = 2 °C, and 2 ÷ 0.2 = 10 spaces.

    2. Describe your drawing and where 37.4 °C goes.

      Show solution

      AnswerFive equal spaces in each degree; 37.4 °C is the second small mark after 37.

      Draw long, numbered marks for 36, 37 and 38 °C, equally spaced. Between 36 and 37, draw 4 short marks so that the degree is cut into 5 equal spaces of 0.2 °C each. Do the same between 37 and 38. Since 37.4 − 37 = 0.4 °C = 2 spaces, the column ends at the 2nd short mark after 37.

  14. Quick answerMediumNCERT Exercises Q14

    Your cousin in Texas sends a message: “Phew, it’s 104 degrees here today!” Which scale is she using?

    Show answer

    Answer (B) Fahrenheit: a very hot day of 40 °C

    Air at 104 °C would be hotter than boiling water, so it cannot be Celsius. 104 K is about −169 °C, far colder than anywhere on the Earth. On the Fahrenheit scale, 104 °F equals 40 °C: a very hot day.
  15. Quick answerMedium

    Liquid nitrogen, which doctors use to freeze warts off the skin, boils at −196 °C. Write this temperature in kelvin.

    K
    Show answer

    Answer 77.15 K

    −196 + 273.15 = 77.15 K.
  16. Quick answerEasy

    The correct way to write three hundred kelvin is 300 °K.

    Show answer

    Answer False

    The degree sign is never used with kelvin. Write 300 K.
  17. Quick answerEasy

    Arrange these from coldest to hottest.

    1. A healthy human body
    2. Water boiling at sea level
    3. Ice cream in a freezer at −18 °C
    4. Melting ice
    5. Absolute zero
    Show answer
    Answer
    1. Absolute zero
    2. Ice cream in a freezer at −18 °C
    3. Melting ice
    4. A healthy human body
    5. Water boiling at sea level
    In °C: −273.15, −18, 0, about 37 and 100.
  18. Quick answerMedium

    On a May day in Jaisalmer, the maximum air temperature was 46 °C and the minimum was 27 °C. What was the difference?

    °C
    Show answer

    Answer 19 °C

    46 − 27 = 19 °C.

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Quick check: MCQs on Temperature and its Measurement

  1. 7.1 Hot or Cold?3 questions
  2. 7.2 Temperature3 questions
  3. Other temperature scales4 questions
  4. 7.3.2 Laboratory thermometer4 questions
  5. 7.3.3 Air temperature3 questions
Glossary · 12

Key terms (English–Hindi)

absolute zeroपरम शून्यparam shoonya
The lowest temperature possible: 0 K, which is −273.15 °C.First seen in the chapter →
air temperatureवायु तापvaayu taap
How hot or cold the air is. Weather reports give each day’s maximum and minimum.First seen in the chapter →
Celsius scaleसेल्सियस पैमानाselsiyas paimaana
The temperature scale used on most thermometers in India. Its unit is the degree Celsius (°C).First seen in the chapter →
clinical thermometerडॉक्टरी थर्मामीटरdoctori tharmameetar
A thermometer for measuring body temperature. Its range is small, about 35 °C to 42 °C.First seen in the chapter →
Fahrenheit scaleफ़ारेनहाइट पैमानाfaarenhait paimaana
A temperature scale whose unit is the degree Fahrenheit (°F). 37.0 °C equals 98.6 °F.First seen in the chapter →
kelvinकेल्विनkelvin
The SI unit of temperature, written K without a degree sign. Kelvin = degrees Celsius + 273.15.First seen in the chapter →
laboratory thermometerप्रयोगशाला तापमापीprayogshaala taapmaapi
A sealed glass tube with a bulb of liquid, used in labs; a common one reads from −10 °C to 110 °C.First seen in the chapter →
normal body temperatureसामान्य शरीर तापsaamaanya shareer taap
The average temperature of healthy people, taken as 37.0 °C (98.6 °F).First seen in the chapter →
rangeपरिसरparisar
The span from the lowest to the highest temperature a thermometer can show.First seen in the chapter →
temperatureतापtaap
A measure of how hot or cold something is. The hotter it is, the higher its temperature.First seen in the chapter →
thermometerतापमापीtaapmaapi
An instrument for measuring temperature.First seen in the chapter →
value of one divisionअल्पतमांकalpatamaank
The temperature change shown by one small space on a scale: difference between two numbered marks ÷ number of spaces.

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