Chapter 7 - Temperature and its Measurement | Class 6 Science

7.1 Hot or Cold?

We know from experience that some bodies are hotter than others[cite: 4]. However, we cannot always rely upon our sense of touch to decide correctly whether a body is hot or cold[cite: 4].

                        Reliability of Touch:

                        In Activity 7.1, when placing one hand in warm water and the other in cold water, and then putting both hands together in tap water, one hand senses it as cool while the other senses it as warm[cite: 4]. This proves our sense of touch is relative and unreliable for accurate judgment[cite: 4].

7.2 Temperature

A reliable measure of hotness (or coldness) of a body is its temperature[cite: 4]. A hotter body has a higher temperature than a colder body[cite: 4]. A device that measures temperature is called a thermometer[cite: 4].

Celsius Scale

Unit: degree Celsius (°C)[cite: 4]. Named in honor of Anders Celsius[cite: 4].

Fahrenheit Scale

Unit: degree Fahrenheit (°F)[cite: 4]. Normal human body temperature is $98.6^{\circ}\text{F}$[cite: 4].

Kelvin Scale (SI Unit)

Unit: kelvin (K)[cite: 4]. The SI unit for temperature[cite: 4]. Degree symbol (°) is not used[cite: 4].

Formula for Conversion (Celsius to Kelvin):
$$\text{Temperature in Kelvin scale} = \text{Temperature in Celsius scale} + 273.15$$[cite: 4]

7.3.1 Clinical Thermometer

A clinical thermometer is used to measure human body temperature[cite: 4]. Modern digital clinical thermometers use heat sensors and operate on batteries, replacing toxic mercury thermometers[cite: 4].

Key Facts & Precautions:

Normal Body Temperature: The normal temperature of a healthy human body is taken to be $37.0^{\circ}\text{C}$ or $98.6^{\circ}\text{F}$[cite: 4].
Human Body Range: Human body temperature does not normally go below $35^{\circ}\text{C}$ or above $42^{\circ}\text{C}$[cite: 4].
Armpit Readings: Temperature measured in the armpit is about $0.5^{\circ}\text{C}$ to $1^{\circ}\text{C}$ lower than actual body temperature[cite: 4].
Non-contact (Infrared) Thermometers: Used to measure body temperature from a distance without physical contact, minimizing disease spread[cite: 4].
Precautions: Wash the tip with soap and water before and after use[cite: 4]. Keep the digital display area out of water[cite: 4]. Do not hold by the tip[cite: 4].

7.3.2 Laboratory Thermometer

Laboratory thermometers are used for general scientific purposes and experiments[cite: 4]. They consist of a long, narrow glass tube with a bulb containing liquid (alcohol or mercury)[cite: 4].

                        Standard Temperature Range: Typical range is from $-10^{\circ}\text{C}$ to $110^{\circ}\text{C}$[cite: 4].
                    

Correct Technique for Laboratory Thermometers:

Hold vertically without tilting[cite: 4].
The bulb must be fully immersed in the liquid without touching the bottom or sides of the beaker[cite: 4].
Read the temperature while the thermometer is still immersed because the liquid column falls immediately upon removal[cite: 4].
Keep eye level directly in line with the top level of the liquid column[cite: 4].

7.3.3 Air Temperature

Air temperature is an essential parameter monitored globally at weather stations for meteorological predictions and forecasts[cite: 4]. Room thermometers give an approximate reading of ambient temperature[cite: 4].

Know a Scientist - Anna Mani (1918–2001):
Known as the 'Weather Woman of India'[cite: 4]. She invented and built a large number of weather measurement instruments, promoting India's self-reliance and research in renewable wind and solar energy[cite: 4].

Chapter Summary

The temperature of a body tells us how hot or cold it is[cite: 4].
The three most used scales of temperature are the Celsius scale (°C), Fahrenheit scale (°F), and Kelvin scale (K)[cite: 4].
The SI unit for temperature is kelvin (K)[cite: 4].
Normal temperature of a healthy adult human body is $37.0^{\circ}\text{C}$ ($98.6^{\circ}\text{F}$)[cite: 4].
A laboratory thermometer typically has a range from $-10^{\circ}\text{C}$ to $110^{\circ}\text{C}$[cite: 4].
Absolute zero is the lowest achievable temperature limit, close to $-273.15^{\circ}\text{C}$ ($0\text{ K}$)[cite: 4].

Exercises & Questions

Q1. The normal temperature of a healthy human being is close to:

Q2. $37^{\circ}\text{C}$ is the same temperature as:

Q3. The range of a laboratory thermometer is usually:

Q4. Fill in the blanks:

1. The hotness or coldness of a system is determined by its temperature[cite: 4].

2. The temperature of ice-cold water cannot be measured by a clinical thermometer[cite: 4].

3. The unit of temperature is degree Celsius / Fahrenheit[cite: 4].

Q5. A laboratory thermometer is not used to measure our body temperature. Give a reason.

Answer: When a laboratory thermometer is removed from the body/mouth, its liquid level immediately starts falling[cite: 4]. Therefore, it does not give an accurate reading outside the body[cite: 4]. Additionally, its scale range is wide and lacks a kink/digital hold mechanism designed for human body measurements[cite: 4].

Q6. A laboratory thermometer has 50 divisions between $0^{\circ}\text{C}$ and $100^{\circ}\text{C}$. What does each division measure?

Answer: Each division measures $\frac{100 - 0}{50} = \mathbf{2^{\circ}\text{C}}$.

Q7. Komal tells you that she has a fever of 101 degrees. Does she mean it on the Celsius scale or Fahrenheit scale?

Answer: She means the Fahrenheit scale (°F)[cite: 4]. A human body temperature of $101^{\circ}\text{C}$ would be fatal and impossible, as normal body temperature is $37^{\circ}\text{C}$ ($98.6^{\circ}\text{F}$)[cite: 4].