Question 1:
Can it always be correctly judged, that a person has fever, only by touching the person?
Answer:
No, we cannot always tell if a person has a fever just by touching them. Our sense of touch is not always reliable. Sometimes, a person’s skin might feel warm or cool for other reasons. To be sure, we need to use a thermometer to measure their body temperature.
Question 2:
Then how do we find out how hot or cold a body is?
Answer:
We use a device called a thermometer to find out how hot or cold something is. A thermometer measures the temperature, which tells us exactly how hot or cold a body is.
Question 3:
Do small children generally have slightly higher body temperatures as compared to adults?
Answer:
Yes, small children often have slightly higher body temperatures than adults. This is normal because their bodies are growing and they may be more active.
Question 4:
Do old people, even when healthy, generally have lower body temperatures than young adults?
Answer:
Yes, older people may have slightly lower body temperatures than younger adults. This can happen because their bodies change as they age.
Question 5:
I have seen a friend of mine using a digital thermometer that reads temperature on a different scale. It shows the normal temperature of a healthy human body as 98.6 °F. What is the reason for this difference?
Answer:
There are different scales for measuring temperature. Your friend’s thermometer uses the Fahrenheit scale, where the normal body temperature is 98.6 °F. On the Celsius scale, the normal body temperature is 37.0 °C. So, 98.6 °F is the same as 37.0 °C.
Question 6:
Can a clinical thermometer be used for measuring the temperature of boiling water? Or for measuring the temperature of ice?
Answer:
No, we should not use a clinical thermometer to measure the temperature of boiling water or ice. Clinical thermometers are designed to measure body temperatures, usually between 35 °C and 42 °C. Boiling water and ice have temperatures outside this range, and using a clinical thermometer could damage it or give incorrect readings.
Question 7:
How can we measure temperatures beyond the range of a clinical thermometer?
Answer:
We can use a laboratory thermometer to measure temperatures beyond the range of a clinical thermometer. Laboratory thermometers can measure temperatures from –10 °C to 110 °C or even higher.
Activity 7.1: Let us investigate
Predict what will you feel if you:
— Dip your right hand in container A (warm water) and left hand in container C (ice-cold water) and keep them there for 1–2 minutes.
— Take out your hands from containers A and C, and place both hands simultaneously in container B (tap water).
Write down your predictions:
— What will my right hand feel on dipping in B?
— What will my left hand feel on dipping in B?
Answer:
Predictions:
- My right hand, which was in warm water, will feel that the water in container B is cool.
- My left hand, which was in ice-cold water, will feel that the water in container B is warm.
Now, conduct the activity and write your observations.
Observations:
- After placing both hands in container B, my right hand felt that the water was cool, and my left hand felt that the water was warm.
Conclusion:
Our sense of touch can be confusing because the same water felt different to each hand. This shows that we cannot always rely on touch to judge temperature accurately.
Activity 7.2: Let us measure
Measure your own temperature as well as the temperature of some of your friends. Record the temperatures in Table 7.1.
Answer:
Table 7.1: Body Temperatures of 10 Persons
| S. No. | Name | Temperature (°C) |
|---|---|---|
| 1 | Myself | 36.8 °C |
| 2 | Friend 1 | 37.0 °C |
| 3 | Friend 2 | 36.9 °C |
| 4 | Friend 3 | 37.1 °C |
| 5 | Friend 4 | 36.7 °C |
| 6 | Friend 5 | 37.2 °C |
| 7 | Friend 6 | 36.6 °C |
| 8 | Friend 7 | 36.9 °C |
| 9 | Friend 8 | 37.0 °C |
| 10 | Friend 9 | 36.8 °C |
Note: The normal body temperature is around 37.0 °C, but it can vary slightly from person to person.
Activity 7.3: Let us observe
Let us try to find the temperature range of a given laboratory thermometer.
— What is the lowest temperature it can measure?
— What is the highest temperature it can measure?
— So, the range of this thermometer is
Answer:
- The lowest temperature it can measure is –10 °C.
- The highest temperature it can measure is 110 °C.
- So, the range of this thermometer is from –10 °C to 110 °C.
Activity 7.4: Let us observe and calculate
Let us now try to find the smallest value that a given laboratory thermometer can read.
— How much is the temperature difference indicated between the two bigger marks?
— How many divisions (shown by smaller marks) are there between these two bigger marks?
— How much temperature does one small division indicate?
— So, the smallest value that the thermometer can read is
Answer:
- The temperature difference between two bigger marks is 10 °C (for example, between 0 °C and 10 °C).
- There are 10 divisions between these two bigger marks.
- Each small division represents 1 °C (10 °C divided by 10 divisions).
- So, the smallest value that the thermometer can read is 1 °C.
Activity 7.5: Let us measure
What is the temperature of water measured by you? Compare it with the readings of your friends.
Do you notice that, as soon as you take the thermometer out of the water, the level of liquid column begins to fall?
Answer:
- The temperature of the warm water I measured was 40 °C.
- My friends also got readings close to 40 °C.
- Yes, when I took the thermometer out of the water, the liquid column started to fall immediately. This is because the thermometer cools down when it’s out of the warm water.
Question:
This means that the temperature must be read while the thermometer is immersed in water.
Answer:
Yes, we should read the temperature while the thermometer is still in the water to get an accurate reading.
Question:
Can we use a laboratory thermometer for measuring body temperature of a person?
Answer:
No, we should not use a laboratory thermometer to measure body temperature. Laboratory thermometers are not designed for this purpose. They don’t have a kink to prevent the liquid from falling, and they can be unsafe for use with people.
Activity 7.6: Let us compare
Compare the temperatures of boiling water recorded by different students.
Why are there differences in their readings? Discuss the possible reasons.
Answer:
- The students recorded slightly different temperatures for boiling water, ranging from 97.8 °C to 98.1 °C.
- The differences could be because:
- They might not have followed the correct method.
- They may have read the thermometer incorrectly.
- Atmospheric pressure and altitude can affect the boiling point of water.
- The thermometers might not be perfectly calibrated.
Activity 7.7: Let us analyse
Read or listen to the weather reports for a place for 10 successive days. Record the maximum and minimum air temperatures in Table 7.3. Analyse the data.
Answer:
Table 7.3: Maximum and Minimum Air Temperatures
| S.No. | Date | Maximum (°C) | Minimum (°C) |
|---|---|---|---|
| 1 | 1st January | 25 | 15 |
| 2 | 2nd January | 26 | 16 |
| 3 | 3rd January | 24 | 14 |
| 4 | 4th January | 25 | 15 |
| 5 | 5th January | 27 | 17 |
| 6 | 6th January | 28 | 18 |
| 7 | 7th January | 29 | 19 |
| 8 | 8th January | 27 | 17 |
| 9 | 9th January | 26 | 16 |
| 10 | 10th January | 25 | 15 |
Analysis:
- The maximum temperatures ranged from 24 °C to 29 °C.
- The minimum temperatures ranged from 14 °C to 19 °C.
- The temperatures changed slightly over the 10 days.
Exercise Questions
Question 1:
The normal temperature of a healthy human being is close to ______.
(i) 98.6 °C
(ii) 37.0 °C
(iii) 32.0 °C
(iv) 27.0 °C
Answer:
(ii) 37.0 °C
Question 2:
37 °C is the same temperature as ______.
(i) 97.4 °F
(ii) 97.6 °F
(iii) 98.4 °F
(iv) 98.6 °F
Answer:
(iv) 98.6 °F
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:
(i) The hotness or coldness of a system is determined by its temperature.
(ii) The temperature of ice-cold water cannot be measured by a clinical thermometer.
(iii) The unit of temperature is degree Celsius.
Question 4:
The range of a laboratory thermometer is usually ______.
(i) 10 °C to 100 °C
(ii) –10 °C to 110 °C
(iii) 32 °C to 45 °C
(iv) 35 °C to 42 °C
Answer:
(ii) –10 °C to 110 °C
Question 5:
Four students used a laboratory thermometer to measure the temperature of water as shown in Fig. 7.6:
Who do you think followed the correct way for measuring temperature?
(i) Student 1
(ii) Student 2
(iii) Student 3
(iv) Student 4
Answer:
(ii) Student 2 followed the correct way. The thermometer should be held vertically, the bulb should be immersed in the water without touching the sides or bottom, and the temperature should be read while the thermometer is in the water.
Question 6:
Colour to show the red column on the drawings of thermometers (Fig. 7.7) as per the temperatures written below: 14 °C, 17 °C, 7.5 °C.
Answer:
- For 14 °C, colour the red column up to the 14 °C mark.
- For 17 °C, colour the red column up to the 17 °C mark.
- For 7.5 °C, colour the red column halfway between 7 °C and 8 °C.
Question 7:
Observe the part of the thermometer shown in Fig. 7.8 and answer the following questions:
(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:
(i) It is a laboratory thermometer.
(ii) The reading of the thermometer is 38 °C.
(iii) The smallest value that this thermometer can measure is 1 °C (if each small division represents 1 °C).
Question 8:
A laboratory thermometer is not used to measure our body temperature. Give a reason.
Answer:
A laboratory thermometer is not used to measure body temperature because:
- It does not have a kink to prevent the liquid from falling when taken out of the mouth.
- It is not designed to be safe for use inside the body.
- It may give inaccurate readings for body temperature.
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.
(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:
(i) Vaishnavi’s highest recorded temperature was 40.0 °C.
(ii) It was recorded on Day One at 7 pm.
(iii) Vaishnavi’s temperature returned to normal on Day Three.
Question 10:
If you have to measure the temperature 22.5 °C, which of the following three thermometers will you use (Fig. 7.9)? Explain.
(a) Thermometer ranging from 35 °C to 42 °C
(b) Thermometer ranging from –10 °C to 110 °C
(c) Thermometer ranging from 0 °C to 50 °C
Answer:
I will use thermometer (c) because:
- Thermometer (a) does not cover 22.5 °C.
- Thermometer (b) could be used, but it may not have the precision needed.
- Thermometer (c) ranges from 0 °C to 50 °C, which includes 22.5 °C and is suitable for this measurement.
Question 11:
The temperature shown by the thermometer in Fig. 7.10 is:
(i) 28.0 °C
(ii) 27.5 °C
(iii) 26.5 °C
(iv) 25.3 °C
Answer:
Assuming the thermometer shows the liquid level halfway between 27 °C and 28 °C:
(ii) 27.5 °C
Question 12:
A laboratory thermometer has 50 divisions between 0 °C and 100 °C. What does each division of this thermometer measure?
Answer:
- Temperature range = 100 °C – 0 °C = 100 °C
- Number of divisions = 50
- Each division measures = 100 °C ÷ 50 = 2 °C
Question 13:
Draw the scale of a thermometer in which the smallest division reads 0.5 °C. You may draw only the portion between 10 °C and 20 °C.
Answer:
[As we cannot draw here, we can explain.]
- Between 10 °C and 20 °C, mark major lines at every 1 °C.
- Between each 1 °C mark, add one smaller line to represent 0.5 °C.
- This means each small division represents 0.5 °C.
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:
She means Fahrenheit scale because a fever of 101 °F is common. A temperature of 101 °C would be extremely high and impossible for the human body.