Temperature and its measurement notes

Temperature and its measurement

Temperature is the measure of how hot or cold something is. It tells us how much heat energy is present in an object, a substance, or the environment. A high temperature means something is hot. A low temperature means something is cold. Temperature and heat are used similarly however, there is a difference between these two as given below

Key Differences Between heat and Temperature

Feature	Heat	Temperature
Definition	Energy transferred due to a difference in temperature	Measure of how hot or cold an object is
Measured in	Joules (J)	Degrees Celsius (C), Fahrenheit (F), or Kelvin (K)
Instrument used	Calorimeter	Thermometer
Depends on	Mass and nature of the substance	Independent of mass or size
Type	Form of energy	Measurement of thermal condition

Temperature is important because it affects:

Our health and comfort
The weather
Our food, medicines, clothes, furniture, surfaces of objects etc.

Some real-life Examples of temperature:

Ramesh and his younger brother Arun live in a small town. One evening, after playing outside for a long time, they returned home. Their parents were busy in the kitchen when Arun suddenly said he was feeling dizzy. Ramesh noticed that Arun looked pale and tired. Ramesh asked his brother to sit down and drink some water. After resting for a while, Arun started to feel better. Ramesh then advised him to stay indoors and rest until he felt completely fine. This example shows how high temperatures or playing too long in the heat can affect our health. It also highlights the importance of being aware of temperature changes and taking simple steps to stay safe and healthy.

Hot or Cold?

We often say things feel hot or cold — but how do we know? When you touch a cup of hot tea, it feels warm. When you hold an ice cube, it feels cold.Our skin helps us feel temperature, but it doesn’t measure it accurately. That’s why we use a thermometer to find the exact temperature of something.

Examples of Hot and Cold Objects

Object	Feels
Boiling water	Hot
Ice cream	Cold
Sunlight in summer	Hot
Cold drink from fridge	Cold
Heater or fire	Hot
Snow	Cold

Fun Fact:

Sometimes, something can feel cold even if it’s not very cold — like metal in winter — because it pulls heat away from your hand quickly!

Hotness or coldness:

From our daily experience, we know that some things feel hotter than others. For example, in summer, the water from the tap might feel warmer than the cool water stored in a matka (earthen pot) or a refrigerator. We can feel the difference just by touching the two types of water. But can we always trust our sense of touch to tell if something is hot or cold.

Temperature

Can temperature tell us how hot or cold something is? Yes, temperature is a reliable way to tell how hot or cold something is. A hotter object has a higher temperature, and a colder object has a lower temperature.

Temperature and Thermometers:

A thermometer is a device used to measure temperature. A good thermometer should be sensitive to temperature; it must have wide Range with clear scale markings. The materials used in the thermometers like mercury, glass and calibre paint should be safe and durable. The device should show accurate and reliable readings.

Common Types of Thermometers:

Thermometer Type	Used For
Clinical Thermometer	Measuring human body temperature
Laboratory Thermometer	Used in science experiments
Digital Thermometer	Used for quick and easy readings
Room Thermometer	Measuring air temperature indoors

Clinical Thermometers

A clinical thermometer is a device used to measure the temperature of the human body. A Clinical Thermometer has:

Bulb: Contains mercury
Capillary Tube: Thin tube through which mercury rises
Constriction: Holds the mercury in place after reading
Scale: Shows temperature markings
Stem: Glass body to hold the thermometer

Feature	Description
Temperature Range	35°C to 42°C (or 94°F to 108°F) – suitable for body temperature
Material	Usually made of glass (older) or plastic (digital type)
Liquid Used	Mercury (in traditional thermometers) or alcohol/digital sensor
Narrow Constriction	Prevents mercury from falling back quickly – helps record reading
Scale	Marked in degrees Celsius (°C) or Fahrenheit (°F)
Length	Short, easy to handle

Steps to use a Clinical Thermometer

Clean the Thermometer by washing it with clean running water or disinfectant. We must wipe it dry with a clean gauge or cotton before use.
Check the Mercury Level by holding the thermometer at eye level against the sunlight.
Make sure the mercury level is below 35°C (or 94°F) by gently shaking the thermometer towards its bulb.
Place the Thermometer Properlyunder the tongue in the mouth. (Alternatively, place it in the armpit for younger children, but mouth gives a more accurate reading.)
Keep the thermometer in place without talking or moving for 1–2 Minutes
Take it out gently. Hold it at eye level and read the temperature on the scale.
Note the body temperature and never forget to record it in the chart for health monitoring.
Wash the thermometer again and store it in soap solution or Dettol solution.

Important safety tips while using thermometer

Handle with Care, especially glass thermometers as they are very delicate and can break easily.
Avoid Biting the thermometer as the mercury is harmful
Children should use thermometers only with adult help and all thermometers should be kept away from childr
If the thermometer cracks or breaks, stop using it immediately. Mercury is toxic. If the thermometer breaks, do not touch mercury with bare hands.
Always clean the thermometer with alcohol or disinfectant like soap solution before and after measuring temperature.
Use Digital Thermometers When Possible because they are safer and easier to use.
Keep the thermometer in a protective case in a safe, cool place.

How do a clinical thermometer works?

When you place the thermometer under your tongue or in the armpit, the body’s heat warms the mercury. Since mercury is a liquid metal sensitive to heat , mercury heats up, it expands and moves up the narrow capillary tube inside the thermometer. The mercury stops rising when the temperature of the body is reached. You can then read the temperature by looking at the scale marked on the glass tube/ The narrow constriction near the bulb holds the mercury in place, so the temperature reading stays until you shake the thermometer. To reuse, you must shake the thermometer sharply to bring the mercury back down below 35°C.

Temperature Scales: Celsius, Fahrenheit, and Kelvin

Temperature is measured using different scales around the world. The three most common are Celsius, Fahrenheit and Kelvin. Kelvin is the S.I Unit of temperature

Celsius (°C) is Most widely used scale worldwide. Water freezes at 0°C and boils at 100°C at normal atmospheric pressure. Used in weather forecasts, cooking, and daily temperature measurements.
Fahrenheit (°F) is mainly used in the hospital settings. Water freezes at 32°F and boils at 212°F. The Fahrenheit scale has smaller degree units than Celsius.

Kelvin (K) is used mainly in science and physics laboratories. It starts at absolute zero (The coldest possible temperature where particles stop moving), which is 0 K. Water freezes at 273 K and boils at 373 K. No degree symbol is used with Kelvin.

Differences between Digital and Mercury Thermometers

Digital Thermometer	Mercury Thermometer
Uses electronic sensors to measure temperature	Uses expansion of mercury to measure temperature
Shows reading on a digital screen	Temperature is read on a marked glass scale
Quick (within seconds)	Takes 1–2 minutes to show accurate reading
Safe – no toxic substance	Contains toxic mercury – can be dangerous if broken
Generally accurate, but depends on battery	Very accurate if used correctly
Needs battery to work	No battery required
Easy to use and read	Needs careful handling and reading
Usually durable (plastic body)	Fragile – made of glass
Slightly more expensive	Usually cheaper

Laboratory Thermometers

A laboratory thermometer is used to measure the temperature of substances in science experiments. It is designed to measure a wide range of temperatures more than a clinical thermometer. It consists of a long, narrow, and uniform glass tube that is sealed at both ends. At one end, there is a bulb filled with a liquid (alcohol or mercury). The liquid column inside the tube rises or falls as the temperature changes. The glass tube has a Celsius scale (°C) marked along its length for reading temperatures. The range of a laboratory thermometer is typically from –10°C to 110°C. No constriction like clinical thermometers – readings must be taken while the thermometer is in the substance.It is used in labs, not for measuring body temperature

Liquid Used in Laboratory Thermometers

Liquid	Details
Alcohol	- Often colored red to make it visible - Used in colder conditions
Mercury	- Appears silvery and shiny - Not colored, but highly accurate

Differences between Clinical Thermometer and Laboratory Thermometer

Clinical Thermometer	Laboratory Thermometer
Measuring human body temperature	Measuring temperature in labs and experiments
35°C to 42°C	-10°C to 110°C
Shorter and has a narrow constriction near the bulb	Longer and no constriction near the bulb
Yes, to prevent mercury from falling back quickly	No, reading must be taken immediately
1 to 2 minutes	Instant while in contact with the substance
Placed under the tongue, armpit, or in the mouth	Placed in liquids or substances (not for human use)
Delicate, meant for careful personal use	Built to withstand lab conditions
Degrees Celsius (°C) or sometimes Fahrenheit (°F)	Usually in Degrees Celsius (°C)

Air Temperature/Atmospheric Temperature

Air temperature tells us how hot or cold the air around us feels. It is one of the most important aspects of weather, and it changes from day to day due to many natural factors like sunlight, wind, clouds, and humidity. In summer, the temperature usually rises but in In winter, the temperature generally drops. We measure air temperature using wall thermometers (used indoors), Digital weather thermometers or Outdoor sensors at weather stations. The data collected includes: Daily high and low temperatures, Temperature trends over time and weather pattern changes. These measurements are essential for making accurate weather forecasts and studying climate change. Measuring atmospheric heat helps people plan clothing, farming, travel, and more.

Question Answers

Question 1. Can it always be correctly judged, that a person has fever, only by touching the person?

Answer

It cannot always be correctly judged that a person has fever, only by touching the person as we are not able to calculate accurate temperature of the body.

If the palm of the hand is cold, the person with normal temperature may be judged with fever.

Also, if the palm of the hand is already warm, the person with fever may be felt at normal temperature.

For correct judgement that a person has fever or not, we must use clinical thermometer correctly.

Question 2. Do small children generally have slightly higher body temperatures as compared to adults?

Answer

Yes, small children usually have slightly higher body temperatures compared to adults because their bodies are working hard to grow quickly, which makes more heat.

For kids, a normal body temperature is usually between 37.0°C and 37.5°C . For adults, it’s a bit lower, usually between 36.1°C and 37.2°C.

Question 3. Do old people, even when healthy, generally have lower body temperatures than young adults? Answer

Yes, even healthy older people generally have lower body temperatures than young adults. As people age, their bodies slow down and don’t produce as much heat. For older adults, normal body temperature is often around 36.2°C to 36.8°C, which is slightly lower than the typical range for younger adults.

Question 4. Can a clinical thermometer be used for measuring the temperature of boiling water? Or for measuring the temperature of ice?

Answer

A clinical thermometer has a range of 35 °C to 42 °C. The temperature of boiling water is 100 °C and is beyond the range of a clinical thermometer. Also the temperature of ice is 0 °C or below, and is beyond the range of clinical thermometer.
Therefore a clinical thermometer cannot used for measuring the temperatures of boiling water or of ice.

Let us enhance our learning

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

37 °C is the same temperature as _____.

(i) 97.4 °F
(ii) 97.6 °F
(iii) 98.4 °F
(iv) 98.6 °F

Answer

(iii) 98.4 °F

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.

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

(i) 10 °C to 100 °C

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

Student 2 measured the temperature of the water by following the correct way, as the thermometer was placed in an upright position without touching the sides or the bottom of the beaker.

Colour to show the red column on the drawings of thermometers (Fig. 7.7) as per the temperatures written below:

Answer

In the first thermometer for 14°C, colour up to two small lines above mark 10 (each small line indicates 2 degrees Celsius).
In the second thermometer for 17°C, colour up to seven small lines above mark 10 (each small line indicates 1 degree Celsius).
In the third thermometer for 7.5°C, colour up to fifteen small lines above mark 0 (each small line indicates 0.5 degree Celsius).

Red lines are marked alongside the respective thermometers for information.

Observe the part of 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) The given thermometer has a minimum temperature marking of -10 degrees. Since laboratory thermometers typically have a temperature range from -10°C to 110°C, this indicates that it is a laboratory thermometer.

(ii) The reading of the thermometer is 26°C.

(iii) Since the minimum temperature marking on the thermometer is -10°C, this is the lowest temperature it can measure.

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

Answer

(i) It has a wide temperature range, from -10°C to 110°C, and the lowest temperature it can measure is 1°C, which makes it unsuitable for detecting small temperature changes in the human body.

(ii) The temperature on a laboratory thermometer must be read while it is in contact with the heat source because, as soon as you remove it, the temperature will begin to decrease rapidly, making it unsuitable for measuring body temperature.

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) 40°C.

(ii) Vaishnavi's highest temperature was recorded at 7 p.m. on the Day one. (iii) Day three.

If you have to measure the temperature 22.5 °C, which of the following three thermometers will you use (Fig. 7.9)? Explain.

Answer

Thermometer (b) would be the best choice, as it has markings that allow for reading half- degree increments, making it possible to accurately measure a temperature of 22.5°C.

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

(ii) 27.5 °C

A laboratory thermometer has 50 divisions between 0 °C and 100 °C. What does each division of this thermometer measure?

Answer

50 divisions of the thermometer = 100°C

1 division of the thermometer = 100°C/50 = 2°C

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

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

Answer

If someone says they have a fever of 101 degrees, they are referring to the Fahrenheit scale Since normal human body temperature is around 37°C, 101°C would be an intolerable temperature for the body to bear.