Answers to the Questions from “Temperature and its Measurement”
1. The normal temperature of a healthy human being is close to:
(ii) 37.0 °C
2. 37 °C is the same temperature as:
(iv) 98.6 °F
3. Fill in the blanks:
(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.
4. The range of a laboratory thermometer is usually:
(ii) –10 °C to 110 °C
5. Who followed the correct way of measuring temperature in Fig. 7.6?
(iii) Student 3
(Student 3 holds the thermometer properly, ensuring no contact with the container’s sides or bottom, and reads it at eye level.)
6. Color the red column of thermometers in Fig. 7.7 as per the temperatures below:
- 14 °C: Fill the red column to a point slightly above halfway between 10 °C and 20 °C.
- 17 °C: Fill the red column slightly above 14 °C, but below 20 °C.
- 7.5 °C: Fill the red column halfway between 5 °C and 10 °C.
7. Observe Fig. 7.8 and answer:
(i) Type of thermometer: Laboratory thermometer.
(ii) Reading of the thermometer: 15.5 °C (if the red column reaches halfway between 15 °C and 16 °C).
(iii) Smallest value it can measure: 0.1 °C (if each small division represents 0.1 °C).
8. Why is a laboratory thermometer not used to measure body temperature?
Laboratory thermometers are designed for a wide temperature range, not the specific range of human body temperature (35 °C–42 °C). Additionally, they lack safety features like a kink to prevent mercury backflow.
9. Vaishnavi’s body temperature record (Table 7.4):
(i) Vaishnavi’s highest recorded temperature: 40.0 °C
(ii) The highest temperature was recorded on Day One at 7 pm.
(iii) Vaishnavi’s temperature returned to normal on Day Three.
10. If you need to measure 22.5 °C, which thermometer would you use (Fig. 7.9)?
(b) The thermometer with a range that includes 22.5 °C and has fine divisions to measure fractional values.
11. The temperature shown in Fig. 7.10 is:
(iii) 26.5 °C
12. A laboratory thermometer has 50 divisions between 0 °C and 100 °C. What does each division measure?
Each division measures:
(100 °C – 0 °C)÷50 divisions=2°C/division.\text{(100 °C – 0 °C)} \div \text{50 divisions} = 2 °C/\text{division}.
13. Draw the scale of a thermometer with divisions reading 0.5 °C (10 °C to 20 °C):
- Mark larger divisions for each degree (10, 11, 12, etc.).
- Divide each degree into two smaller divisions (0.5 °C each).
- Label the smaller increments (e.g., 10.5 °C, 11.5 °C).
14. Someone says they have a fever of 101 degrees. Is this Celsius or Fahrenheit?
This refers to the Fahrenheit scale, as 101 °C would indicate an extremely high and fatal fever.
Learning Further (Suggested Activities):
(i) Body temperature of animals:
Body temperatures of animals are often measured using digital thermometers designed for rectal, oral, or ear use. For example:
- Cat: ~38.1 °C to 39.2 °C
- Dog: ~37.5 °C to 39.2 °C
- Horse: ~37.2 °C to 38.5 °C
Visit a veterinary hospital to observe the methods firsthand.
(ii) Coldest and hottest places in India:
- Coldest place: Dras, Ladakh (~ –45 °C recorded).
- Hottest place: Phalodi, Rajasthan (~ 51 °C recorded).
(iii) Temperatures of planets in the Solar System:
Create a table of planets, their average distances from the Sun, and their surface temperatures. For instance:
- Mercury: Closest to the Sun, ~430 °C during the day.
- Venus: High greenhouse effect, ~462 °C.
More to Know:
- The Sun’s core temperature reaches ~15 million °C.
- Absolute zero, the lowest possible temperature, is –273.15 °C (0 K).
Answers to the Activities and Questions on Temperature and its Measurement
1. Can it always be correctly judged that a person has a fever only by touching the person?
No, our sense of touch is subjective and not always reliable for determining if someone has a fever. For accurate measurement, a thermometer is necessary.
2. What do you infer from Activity 7.1?
The sensation of hotness or coldness depends on the temperature difference between the object and our skin. When both hands are placed in water (container B), they perceive different temperatures due to prior exposure to hot or cold water. This shows that touch alone cannot reliably determine temperature.
3. Why is temperature a reliable measure of hotness?
Temperature provides a consistent, quantifiable measurement of hotness or coldness using scientific scales, making it more accurate than subjective touch.
4. What is a thermometer? Name the types of thermometers.
A thermometer is a device used to measure temperature.
Types of thermometers:
- Clinical thermometer (for body temperature)
- Laboratory thermometer (for experimental purposes)
- Digital thermometer
- Infrared thermometer
5. What precautions should be taken while using a digital clinical thermometer?
- Wash the tip before and after use with soap and water.
- Avoid immersing the digital display in water.
- Do not hold the thermometer by its tip.
- Follow the instruction manual for correct usage.
6. Why is the normal body temperature not always 37.0 °C for everyone?
The normal body temperature of 37.0 °C is an average based on healthy individuals. Factors like age, activity level, time of day, and individual differences can lead to slight variations.
7. Can a clinical thermometer be used to measure boiling water or ice temperature?
No, the temperature range of a clinical thermometer (usually 35 °C to 42 °C) does not include the temperatures of boiling water or ice.
8. What are the differences between Celsius, Fahrenheit, and Kelvin scales?
| Aspect | Celsius Scale | Fahrenheit Scale | Kelvin Scale |
|---|---|---|---|
| Unit | °C | °F | K |
| Normal Body Temp | 37.0 °C | 98.6 °F | 310.15 K |
| Water Freezing Point | 0 °C | 32 °F | 273.15 K |
| Water Boiling Point | 100 °C | 212 °F | 373.15 K |
9. Why are digital thermometers replacing mercury thermometers?
- Mercury thermometers pose health and environmental risks if broken, as mercury is toxic.
- Digital thermometers are safer, easier to read, and more accurate.
10. What are the typical ranges of a laboratory thermometer?
The range of a laboratory thermometer is usually from –10 °C to 110 °C.
11. Why is it important to hold a laboratory thermometer vertically and avoid touching the bulb to the container’s sides?
Holding it vertically ensures an accurate reading, and avoiding contact with the container’s sides prevents external influences on the liquid column inside the thermometer.
12. Why does the liquid column in a thermometer fall when removed from water?
The liquid column falls because the thermometer starts losing heat to the surrounding air, causing the temperature reading to drop.
13. Why does the temperature of boiling water or melting ice remain constant?
The temperature remains constant during boiling or melting because the heat is used to change the state (from liquid to gas or solid to liquid) instead of raising the temperature.
14. What are the differences in readings of boiling water in Activity 7.6? Why?
The differences occur due to:
- Variations in how students handle the thermometer.
- Atmospheric pressure differences affecting boiling points.
15. What precautions should be taken while performing experiments with laboratory thermometers?
- Handle with care to prevent breakage.
- Avoid touching the bulb to the container’s sides or bottom.
- Read the thermometer at eye level while it is immersed.
- Perform experiments under supervision.
16. Why do weather reports provide maximum and minimum temperatures?
These temperatures help monitor daily variations in weather, providing insights into the climate and trends such as warming or cooling.
17. What are the uses of the Kelvin scale in science?
The Kelvin scale is used in scientific studies because it starts at absolute zero (the lowest possible temperature) and simplifies calculations in thermodynamics and physics.
18. Can a laboratory thermometer be used for measuring body temperature?
No, a laboratory thermometer cannot be used to measure body temperature because it lacks the features required for safe and accurate human use, like a specific range and safety measures.
19. Record temperatures of boiling water and crushed ice.
- Boiling water: Approx. 100 °C (may vary slightly with altitude).
- Crushed ice: Approx. 0 °C.
20. How does Anna Mani’s work influence weather measurement today?
Anna Mani’s development of weather instruments made India self-reliant in meteorology and advanced its capabilities in renewable energy. Her contributions to precision instruments are vital for accurate weather forecasting globally.
Summary
- Temperature is a reliable indicator of hotness or coldness.
- Clinical thermometers measure body temperature; laboratory thermometers are used for experimental purposes.
- The normal body temperature is approximately 37.0 °C or 98.6 °F.
- Mercury thermometers are being replaced by safer, digital alternatives.
- Understanding temperature variations is crucial for health and weather forecasting.
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