Chapter Notes: Temperature and its Measurement

Introduction 

Temperature is a measure of how hot or cold something is. It tells us about the amount of heat energy present in an object or the environment. Temperature is important because it affects our daily lives in many ways. For example, it determines the weather, affects how food is cooked, and even influences how we feel. 

For Example, Rohan and his younger brother Amit live in a small town. One evening, they returned home after playing outside. Their parents were busy in the kitchen, and Amit mentioned that he was feeling dizzy. Rohan noticed that Amit looked pale and tired. To make sure everything was fine, Rohan asked him to sit down and drink some water. After a while, Amit felt better. Rohan then told him to take a rest and avoid going outside again until he felt fully recovered.

Hot or Cold?

Can we always trust our sense of touch to tell if something is hot or cold?

We can often feel if something is hot or cold by touching it, like how tap water feels warmer than water from a clay pot in summer. But, we can’t always trust our skin to tell the exact temperature. Sometimes, our sense of touch can be tricky, so it’s better to use a thermometer to accurately measure how hot or cold something is!

Discussing how we feel temperature:

• 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.

Try yourself:

Which of the following situations illustrates the limitation of relying solely on the sense of touch to determine temperature accurately?

• A.Touching a metal object left in the sun and feeling it very hot.
• B.Feeling tap water in summer to be hotter than water from a clay pot.
• C.Touching ice cream and feeling it cold.
• D.Feeling cool water from a clay pot to be colder than it actually is.

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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.

About Temperature and Thermometers:

• Temperature  is a reliable measure of how hot or cold an object is. A hotter object has a higher temperature than a colder one. The difference in temperature between two objects indicates how much hotter one is compared to the other.
• A device used to measure temperature is called a  thermometer. There are two main types:
  1. Clinical Thermometers: These are used to measure the temperature of the human body.
  2. Laboratory Thermometers: These are used for various other purposes in scientific settings.

Measuring Temperature

1. Clinical Thermometers

Can you explain how a clinical thermometer works to measure body temperature?

A clinical thermometer, also known as a digital thermometer, is used to measure body temperature. It works by placing it on the skin, and it quickly measures and displays the temperature on a digital screen. The temperature is shown in degrees Celsius (ºC). These thermometers are powered by batteries and are commonly used to check if someone has a fever!

How Clinical Thermometers work:

• Clinical thermometers, also known as digital clinical thermometers, are devices used to measure body temperature. 
• They display temperatures digitally and are powered by batteries. 
• These thermometers measure temperature when placed in contact with a person’s body. 
• Clinical thermometers work by using a scale called the Celsius scale. 
• Temperature is measured in degrees Celsius, represented by the symbol ºC. 
• When the thermometer is placed against the skin, it quickly measures and displays the body’s temperature. 

Temperature Scales: Fahrenheit and Kelvin

• Fahrenheit Scale: The Fahrenheit scale measures temperature in degrees Fahrenheit (°F). For example, a temperature of 37.0°C on the Celsius scale is equivalent to 98.6°F on the Fahrenheit scale. 
• Usage: The Fahrenheit scale is becoming less common in scientific studies. 
• Kelvin Scale:  The Kelvin scale is used in scientific work, where temperature is measured in kelvins (K). 
• SI Unit: The Kelvin is the SI unit for temperature. 

Differences between Digital and Mercury Thermometers 

• Mercury thermometers  were once commonly used to measure body temperature, but they pose risks because mercury is a toxic substance. If the thermometer breaks, disposing of it safely can be difficult. 
• Digital thermometers are now preferred because they do not contain toxic materials and are safer to use. Additionally, the numbers displayed on digital thermometers are easier to read. 
• Digital thermometers use  heat sensors  to accurately measure temperature, making them a reliable and convenient choice for monitoring body temperature. 

Converting Celsius to Kelvin Temperature Scale 

• To convert from the Celsius scale to the Kelvin scale, you can use the following formula: 
• Temperature in Kelvin = Temperature in Celsius + 273.15 
• This means that you add 273.15 to the temperature in Celsius to get the temperature in Kelvin. 
• Example: 
  •  If the temperature is 25 degrees Celsius, to convert it to Kelvin: 
  •  Temperature in Kelvin = 25 + 273.15 = 298.15 K

Temperature Scales and Units

• Temperature scales are named after people:  Celsius scale,  Fahrenheit scale, and  Kelvin scale. The names of these scales always start with a  capital letter  . 
• When we write the units for temperature, like  degree Celsius  and  degree Fahrenheit, the word  degree  starts with a  small letter, but Celsius and Fahrenheit  start with a  capital letter. For the unit  kelvin , it always starts with a  small letter  . 
• The symbols for these units are written in capital letters:  °C ,  °F , and  K. Remember, we do not use the degree sign (°) with the symbol  K  . 
• When writing the symbols, we do not put a full stop after them unless it is the end of a sentence. Also, when we write the temperature, we leave a space between the number and the unit. For example, we write 30 °C, not 30°C. 
• If the temperature is more than one degree, we use the plural form of ‘degree’, which is ‘degrees’. For example, we write ’20 degrees Celsius’ as ’20 °C’. 

Fever Detection Before Thermometers

• Before the invention of thermometers, people used the pulse rate to help detect fever. In ancient India, it was known that fever could increase a person’s pulse rate. 
• However, pulse rate alone was not a reliable indicator of fever because other situations could also affect the pulse rate. 
• For example, physical activity, emotional stress, and other conditions could also cause an increase in pulse rate. 

2. Laboratory Thermometers 

• Laboratory thermometer consists of a long, narrow, and uniform glass tube that is sealed at both ends. 
• At one end of the tube, there is a bulb containing a liquid. Outside the bulb, within the tube, there is a narrow column of liquid that is visible.
• The glass tube is marked with a Celsius scale along its length. This scale is used to measure temperature. 

Liquid Used in Laboratory Thermometers 

The liquid commonly used in laboratory thermometers is either alcohol or mercury. 

• Alcohol: Alcohol is often colored red to make it easily visible in the thermometer. 
• Mercury: Mercury is another liquid used in thermometers, but it is not colored. 

3. Air Temperature

Do you think the maximum and minimum temperatures stay the same every day? 

Not really! Weather changes due to many factors, so these temperatures can be different each day. Generally, as we move into summer, the temperature goes up, and in winter, it goes down.

Air Temperature and How we Measure It:

• Air temperature is an important aspect of weather that tells us how hot or cold the air is around us. We can measure air temperature using special tools called thermometers.
• When you see a thermometer, like the one in the picture above, you can tell if the room is warm, cool, or just right. These thermometers are often found in places like schools, doctors’ clinics, and hospitals to help people know the temperature inside.

Measuring Air Temperature: Techniques and Importance 

• Various techniques are used to  measure air temperature , which is a crucial weather parameter monitored globally at  weather stations. 
• The data collected on air temperature, along with other parameters, is essential for making accurate  weather forecasts . 

Key Notes

1. Temperature: A measure of how hot or cold an object is.
2. Thermometers: Devices used to measure temperature accurately.
3. Types of Thermometers: Include clinical thermometers (digital and mercury) and laboratory thermometers.
4. Temperature Scales: Celsius, Fahrenheit, and Kelvin scales are commonly used.
5. Measurement Techniques: Proper methods for using clinical and laboratory thermometers.
6. Body Temperature Variations: Influenced by age, activity level, and time of day.

Try yourself:What is the liquid commonly used in laboratory thermometers?

• A.Water
• B.Petrol
• C.Oil
• D.Mercury

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