NCERT Solutions for Class 6 Science Chapter 7 Temperature and Its Measurement (PDF) – 2027

No. Touching gives only a rough idea. The feeling depends on whether our own hand is warm or cold, so it can be wrong, and it never tells us how much the temperature is. In the story, Phiban felt that Lambok had fever, but the thermometer showed that his temperature was normal. Fever can be confirmed only by measuring the temperature with a thermometer.

Prediction: the right hand will feel that the water in B is cool (cold), because this hand has just come out of the warm water in A, and the tap water in B is cooler than that.

Prediction: the left hand will feel that the water in B is warm, because this hand has just come out of the ice-cold water in C, and the tap water in B is warmer than that.

Observation: the predictions come true. Water in B is a single sample at a single temperature, yet

Conclusion: Our sense of touch cannot always be relied upon to decide correctly whether a body is hot or cold.

Yes — the observations match the predictions. The right hand felt B cool and the left hand felt the same water warm.

The inference:

By measuring its temperature with a thermometer.

• Temperature is a reliable measure of the hotness (or coldness) of a body.
• A hotter body has a higher temperature than a colder body.
• The difference in temperature between two bodies tells us how much hotter one is than the other.
• The device that measures temperature is called a thermometer.

They were non-contact thermometers, also called infrared thermometers. They can measure a person’s temperature from a distance, without touching the body, and so they reduce the risk of spreading disease.

(your own table will have your classmates’ names and their own readings):

Notice that the ten readings are not all the same, but they all lie close to 37.0 °C — between about 36.6 °C and 37.3 °C here.

No, every person did not read exactly 37.0 °C. Some readings were slightly higher and some slightly lower (in the sample Table 7.1 above, from 36.6 °C to 37.3 °C), although everyone was healthy. This is because 37.0 °C is only the average body temperature of a large number of healthy people. Body temperature also depends on age, time of the day and activity level.

Yes. Small children generally have a body temperature that is a little higher than that of adults — often a few tenths of a degree Celsius above the adult average.

Yes. Healthy old people generally show a body temperature that is slightly lower than that of young adults.

This is why the book says a perfectly healthy person may have a normal temperature slightly different from 37.0 °C, and lists age as one of the factors that influence it.

Because that thermometer is showing the same temperature on a different scale — the Fahrenheit scale, whose unit is degree Fahrenheit, written °F.

No. The temperatures of boiling water and of ice are outside the range of a clinical thermometer.

For ice and boiling water we must use a laboratory thermometer, whose range is –10 °C to 110 °C.

By using a laboratory thermometer.

• The one usually kept in a school laboratory has a range of –10 °C to 110 °C.
• That single stretch covers ice at 0 °C, room air, warm water, and water boiling at about 100 °C.
• It is a long sealed glass tube with a bulb of liquid (alcohol coloured red, or mercury) at one end and a Celsius scale marked along the tube.

By feeling the pulse rate of the person.

• Fever affects the pulse rate — it usually makes the pulse faster.
• This was known even in olden days in India, and a physician would judge illness by holding the patient’s wrist.

But this method has a weakness: apart from fever, some other situations also affect the pulse rate — running, fear, excitement, exercise. Hence pulse rate alone is not a reliable indicator of fever.

For the laboratory thermometer shown in Fig. 7.3a, the lowest mark on the scale is –10 °C.

To find it on your own thermometer, hold it upright and look at the bottom end of the scale, just above the bulb. The first number printed there is the lowest temperature it can measure.

For the thermometer in Fig. 7.3a, the highest mark on the scale is 110 °C.

It is found at the top end of the scale, farthest from the bulb.

The range of a thermometer is written as “lowest mark to highest mark”.

So the thermometer of Fig. 7.3a can measure any temperature from –10 °C to 110 °C, and no temperature outside it.

On the thermometer of Fig. 7.3b, the bigger (numbered) marks are 0 °C, 10 °C, 20 °C, 30 °C and so on.

So the temperature difference indicated between two neighbouring bigger marks is 10 °C.

Count the small gaps, not the small lines. Between 0 °C and 10 °C on the thermometer of Fig. 7.3b there are 10 divisions.

Divide the temperature difference by the number of divisions.

The smallest value that this thermometer can read is 1 °C.

Yes — it is 1 °C. Here is the whole calculation in one place:

The temperature of the warm water measured by me was 45 °C. My friends measured the same water as 45 °C, 44 °C and 45 °C. So our readings were very close to one another, but not all exactly the same.

Yes. As soon as the thermometer is taken out of the warm water, the liquid column starts to fall, because the bulb begins to cool in the air. So the temperature must be read while the thermometer is still immersed in the water.

No, it should not be used for that. Here is why, point by point:

Reasons: (1) its liquid column starts falling as soon as it is taken out of the mouth, and it cannot be read while it is inside the mouth; (2) it usually reads only to 1 °C, while body temperature must be known to 0.1 °C (37.6 °C and 38.4 °C would both look like 38 °C); (3) it is long and breaks easily.

Read the two laboratory thermometers, keeping your eye in line with the top of each liquid column.

These are the standard values at sea level. In your own classroom the boiling water may read a little less than 100 °C.

They are the same — the readings have not changed.

• The temperature of water remains constant while it is boiling, even though the burner keeps supplying heat.
• The temperature of ice remains constant while it is melting, even though the room keeps supplying heat.

The readings are very close to one another, but not all the same. They lie between 97.8 °C (Phiban) and 98.1 °C (Bandarisha), a difference of only 0.3 °C, and all are close to 98 °C. Shemphang and Kloi recorded exactly the same value, 98.0 °C. All the readings are a little below 100 °C.

Maybe the correct way of reading temperature was not followed by all the students. For example, some may not have kept their eye in line with the top of the liquid column, some may have taken the thermometer out of the water before reading it, or let the bulb touch the bottom or side of the vessel, or read it before the column stopped rising.

(Jaipur, ten days in February — your own table will have your own place and dates):

Analysing this data:

• Highest maximum = 29 °C (10 Feb); lowest maximum = 22 °C (7 Feb).
• Highest minimum = 15 °C (10 Feb); lowest minimum = 8 °C (7 Feb).
• The daily difference (maximum – minimum) stays around 13 °C to 14 °C.
• Over the ten days both the maximum and the minimum are slowly rising — winter is giving way to summer.

No. Both the maximum and the minimum temperature change from day to day, because weather depends on several factors. Generally, as we approach the summer season the temperature rises, and during the winter season it falls.

Answer: (ii) 37.0 °C — the normal temperature of a healthy human body is taken to be 37.0 °C. (98.6 is its value in °F, not in °C.)

Answer: (iv) 98.6 °F — a temperature of 37.0 °C on the Celsius scale is equivalent to 98.6 °F on the Fahrenheit scale.

(ii) Ice-cold water is at about 0 °C, far below the range of a clinical thermometer, which is made only for body temperatures (about 35 °C to 42 °C). So a clinical thermometer cannot measure it. A laboratory thermometer (–10 °C to 110 °C) can.

Answer: (ii) –10 °C to 110 °C — a laboratory thermometer has to measure temperatures from a little below that of melting ice (0 °C) to a little above that of boiling water (about 100 °C).

Answer: (ii) Student 2 — Student 2 holds the thermometer vertically, with the bulb fully in the water and not touching the bottom or the sides of the beaker. Student 1 holds it tilted, Student 3’s bulb touches the bottom and Student 4’s bulb touches the side of the beaker.

• 14 °C on the first thermometer — 2 divisions above the 10 °C mark (10 + 2 + 2 = 14).
• 17 °C on the second — 7 divisions above the 10 °C mark.
• 7.5 °C on the third — 15 divisions above the 0 °C mark (15 × 0.5 = 7.5).

(i) It is a laboratory thermometer, because its scale starts below 0 °C (at –10 °C) and goes beyond 40 °C.

(ii) The reading is 26 °C — the red column ends 6 small divisions (6 °C) past the 20 °C mark.

(iii) The smallest value it can measure is 1 °C — 10 small divisions lie between 0 °C and 10 °C, so one division = 10 °C ÷ 10 = 1 °C.

Reason: the liquid column of a laboratory thermometer starts falling as soon as it is taken out, so it must be read while its bulb is still in contact with what is being measured. It cannot be read while it is inside a person’s mouth, and once it is taken out the reading is lost.

(i) The highest recorded temperature was 40.0 °C. Scanning all eighteen readings, the largest is 40.0 °C; the next largest are the three readings of 39.0 °C on Day Two.

(ii) It was recorded on Day One at 7 pm.

(iii) On Day Three — on that day her temperature came down to the normal 37.0 °C (at 4 pm).

Answer: thermometer (b).

Explanation to write: a thermometer can only be read to its smallest division. Thermometer (b) has the finest divisions, 0.5 °C, and 22.5 °C lands exactly on one of its marks. On (a) 22.5 °C lies halfway between two marks, and on (c) it lies between 22 °C and 24 °C — neither can show it correctly.

Answer: (ii) 27.5 °C

So each division of this thermometer measures 2 °C.

She means 101 °F, on the Fahrenheit scale. It cannot be 101 °C, because human body temperature does not normally go above 42 °C (water itself boils at about 100 °C). On the Fahrenheit scale normal body temperature is 98.6 °F, so 101 °F means she has a fever.

A veterinary doctor usually measures an animal’s body temperature with a digital clinical thermometer. Its tip is gently put into the animal’s rectum (back passage) and kept there for about a minute; the mouth is not used. Some vets also use a non-contact infrared thermometer for a quick check.

Approximate normal body temperatures to compare your findings with (all in °C):

Coldest: Dras in Ladakh, often called the coldest inhabited place in India (temperatures near –45 °C have been recorded), and the Siachen Glacier.
Hottest: Phalodi in Rajasthan, where about 51 °C was recorded in May 2016; Churu and Bikaner (Rajasthan) also often cross 47 °C in summer.

Here is the table, with the planets in increasing order of distance:

Yes — as a general rule, the farther a planet is from the Sun, the colder it is. From Earth outwards the temperature falls steadily, all the way to about –200 °C at Neptune.

But there is one clear exception: Venus. Venus is farther from the Sun than Mercury, yet it is by far the hottest planet — about 464 °C against Mercury’s 167 °C.

Sample record for one day (make a fresh row for each day, for two weeks):

Conclusion (sample): Both readings rise from morning to afternoon. The water temperature follows the room temperature but changes more slowly — a little higher than the air in the cool morning and a little lower in the hot afternoon.