CHAPTER- 7 TEMPERATURE AND ITS MEASUREMENT
Notes
1. We know from our experience that some objects are hotter or colder than other objects. We feel this through touch.- To determine whether an object is hot or cold, we cannot always rely on our sense of touch.
2. Heat— The reliable measure of the hotness (or coldness) of a body is its temperature.
- The temperature of a hot body is higher than that of a cold body.
- The instrument that measures temperature is called a thermometer.
- To measure temperature, you may have used two types of thermometers— a clinical (doctor’s) thermometer and a laboratory thermometer.
3. Clinical thermometer— It is used to measure our body temperature. These thermometers are also called electronic clinical thermometers or digital clinical thermometers.
- When kept in contact with a person’s body, these thermometers measure the body temperature.
- The scale generally used in a clinical thermometer to measure temperature is the Celsius scale. The unit of temperature on this scale is degree Celsius, denoted by °C.
- The normal temperature of a healthy human body is considered to be 37.0 °C.
4. Another scale of temperature is the Fahrenheit scale. On this scale, the unit of temperature is degree Fahrenheit, denoted by °F.
- A temperature of 37.0 °C measured on the Celsius scale is equivalent to 98.6 °F on the Fahrenheit scale.
5. For scientific work, another scale of temperature is used, called the Kelvin scale. On this scale, the unit of temperature is the kelvin, denoted by K.
- The SI unit of temperature is kelvin.
LET US ENHANCE OUR LEARNING
Question- 1. The normal temperature of a healthy human being is close to ______.
1) 98.6 °C
2) 37.0 °C
3) 32.0 °C
4) 27.0 °C
Answer- 2) 37.0 °C
Question- 2. 37 °C is the same temperature as _________.
1) 97.4 °C
2) 97.6 °F
3) 98.4 °F
4) 98.6 °F
Answer- 4) 98.6 °F
Question- 3. Fill in the blanks:
1) The hotness or coldness of a system is determined by its ________.
2) The temperature of ice-cold water cannot be measured by a __________ thermometer.
3) The unit of temperature is degree _______.
Answer- 1) Temperature, 2) Clinical thermometer, 3) Celsius.
Question- 4. The range of a laboratory thermometer is usually ______.
1) 10 °C
2) -10 °C to 110 °C
3) 32 °C to 45 °C
4) 35 °C to 42 °C
Answer- 2) -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?
1) student 1
2) student 2
3) student 3
4) student 4
Answer- 2) Student 2
Student 2 has suspended the thermometer in the middle of the beaker so that the bulb of the thermometer is completely immersed in the water and is not touching any surface or wall of the beaker. This is the correct procedure by which the accurate temperature of the water can be measured.
Question- 6. Colour to show the red column on the drawings of thermometers (fig. 7.7) as per the temperatures written below.
Answer- 
Question- 7. Observe the part of thermometer shown in fig. 7.8 and answer the following questions:
2) what is the reading of the thermometer?
3) what is the smallest value that this thermometer can measure?
Answer- 1) This is a laboratory thermometer.
2) The reading of this thermometer is 26.0 °C.
3) The minimum value that can be measured by this thermometer is -10 °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 its measuring range is from -10 °C to 110 °C. Since the normal human body temperature is 37 °C, a narrow measuring range of the thermometer is required to measure body temperature accurately.
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.
Table 7.4: Body temperature record of Vaishnavi
2) on which day and at what time was Vaishnavi's highest temperature recorded?
3) on which day did Vaishnavi's temperature return to normal?
Answer- 1) Vaishnavi’s recorded maximum temperature was 40.0 °C.
2) Vaishnavi’s maximum temperature was recorded on the first day at 7 p.m.
3) Vaishnavi’s temperature became normal on the third day, when it fell below 37.0 °C.
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.
Question- 11. The temperature shown by the thermometer in fig. 7.10 is
1) 28.0 °C
2) 27.5 °C
3) 26.5 °C
4) 25.3 °C
Answer- 2) 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- Total measuring range of temperature = 100 °C − 0 °C = 100 °C
Total divisions = 50
Temperature per division = 100 °C /50 = 2 °C
Therefore, each division of the thermometer measures 2 °C.
Question- 13. Draw the scale of a thermometer in which the smallest reads 0.5 °C. You may draw only the portion between 10 °C and 20 °C.
Answer- 
Question- 14. Komal tells you that she has a fever of 101 degrees. Does she mean it on the celsius scale or fahrenheit scale?
Answer- Whenever someone says that they have a fever of 101 degrees, they mean it on the Fahrenheit scale. Converting 101 degrees Fahrenheit to Celsius gives approximately 38.3 °C, which corresponds to the symptoms of a fever. If this temperature were in Celsius, it would be extremely high and life-threatening.
