NCERT Solutions Curiosity Chapter 7 Correct way of measuring temperature using a laboratory thermometer — Activity 7.5: Let us measure
Book page 132 Updated on2026-09-05
Q1.
What is the temperature of water measured by you? Compare it with the readings of your friends.
Answer
Do it exactly as the book describes and then write down what your thermometer shows.
Take some warm water in a beaker.
Dip the thermometer so that the bulb is fully immersed in the water, but does not touch the bottom or the sides.
Hold it vertically and watch the liquid column rise.
Wait until the column stops rising — but do not wait too long, or the water itself will begin to cool.
Read the mark that the top of the liquid column touches, keeping your eye in line with it, while the thermometer is still in the water.
Reading a laboratory thermometer. The eye must be exactly in line with the top of the liquid column; looking from above or from below gives a wrong reading. The bulb stays fully in the water but does not touch the bottom or the sides.
Sample answer: “The temperature of the warm water measured by me was 45 °C.” Three friends measuring the same beaker got 45 °C, 44 °C and 45 °C.
Why the readings differ a little: the water keeps cooling all the time, so a friend who measured a minute later gets a slightly lower value. Also, the thermometer can only be read to its smallest value — 1 °C for the usual laboratory thermometer — so a true 44.6 °C will be written by one student as 45 °C and by another as 44 °C.
Q2.
Do you notice that, as soon as you take the thermometer out of the water, the level of liquid column begins to fall?
Answer
Yes. The moment the thermometer leaves the warm water, the liquid column starts sliding down.
Why it happens: the liquid in the bulb expands when it is heated and contracts when it cools. Out in the open the bulb begins losing heat to the cooler air at once, the liquid contracts, and the column falls. A laboratory thermometer has no kink to hold the liquid in place, so nothing stops it from running back into the bulb.
Therefore:the temperature must be read while the thermometer is still immersed in the water.
Tip: This is the one big difference from a clinical thermometer. A clinical thermometer can be taken out and read at leisure, because the kink above its bulb keeps the thread of mercury from slipping back.