NCERT Solutions Curiosity Chapter 7 .3.2 Laboratory thermometer — Activity 7.6: Let us compare
Book page 1337 Updated on2026-09-05
Q1.
Compare the temperatures of boiling water recorded by different students (Table 7.2).
Answer
The five readings taken in Shillong were:
Name
Temperature of boiling water (in °C)
Phiban
97.8
Shemphang
98.0
Onestar
97.9
Kloi
98.0
Bandarisha
98.1
Now compare them:
Lowest reading = 97.8 °C (Phiban) Highest reading = 98.1 °C (Bandarisha) Spread = 98.1 °C – 97.8 °C = 0.3 °C Sum = 97.8 + 98.0 + 97.9 + 98.0 + 98.1 = 489.8 Average = 489.8 ÷ 5 = 97.96 °C, that is about 98.0 °C
So all five readings agree closely — they differ by at most 0.3 °C — and they cluster around 98.0 °C. Two students (Shemphang and Kloi) got exactly the same value.
Q2.
Why are there differences in their readings? Discuss the possible reasons amongst yourselves.
Answer
As the book says, maybe the correct way of reading temperature was not followed by all the students. The likely reasons are:
The eye was not in line with the top of the liquid column — looking from above or below shifts the reading (this is the commonest mistake).
The thermometer was taken out of the water before reading, so the column had already started to fall.
The bulb touched the bottom or the side of the vessel, so it measured the hot glass rather than the water.
The reading was taken too early, before the liquid column stopped rising.
Each student can only read up to the smallest value of the thermometer, so a true 97.95 °C gets written as 97.9 °C by one student and 98.0 °C by another.
Why the whole group is below 100 °C: that part is not a mistake. Shillong stands high in the hills, where the air pressure is lower, so water there really does boil at about 98 °C. The small differences within the group come from how it was measured; the gap from 100 °C comes from where it was measured.
Tip: When several people measure the same thing, take the average. Here the average, 97.96 °C, is a better answer than any single reading.