Temperature and its Measurement
Chapter Notes | Science Olympiad Class 6
1. Understanding Temperature and Thermometers
Have you ever touched an ice cube and felt the chill, or placed your hands near a flame and sensed the heat? Why do some things feel cold while others feel hot?
One evening, Shruti and her younger brother Amit returned home after playing outside. Amit looked pale and tired, and their parents noticed that he seemed unwell. To check whether he had a fever, they used a thermometer, which showed that he had a fever. He was advised to rest and drink plenty of water.
Just as Amit's parents used a thermometer to check his fever, scientists and doctors use thermometers to measure how hot or cold things are. In this chapter, we will learn about temperature, different kinds of thermometers, and how they work.
Hot or Cold?
Can we always trust our sense of touch to tell us whether something is hot or cold?
Not always. Our skin can be tricked. For example, a metal spoon may feel much colder than a wooden spoon even when both are at the same temperature. After our hands have been warmed by the Sun, water at normal room temperature may feel very cold. These differences occur because different materials transfer heat to or from our skin at different rates and our sensation also depends on what our hands have touched earlier.
Our sense of touch is useful for getting a quick idea about temperature, but it does not give an exact reading. The material, its ability to conduct heat, and our own body temperature affect how hot or cold something feels. Therefore, we use a thermometer for accurate measurement.
Temperature
Temperature is a measure of how hot or cold an object is. It is related to the average kinetic energy of the particles in the object. At a higher temperature, the particles move faster on average; at a lower temperature, they move more slowly on average.
Heat flows from a hotter object to a colder object until both objects reach the same temperature. This condition is called thermal equilibrium.
Understanding temperature and its measurement is important in daily life, healthcare, cooking, science experiments, and weather forecasting.
What Is a Thermometer?
A thermometer is an instrument used to measure temperature accurately. It detects a temperature-related change and displays the temperature on a scale or screen.
Two main groups of thermometers commonly used in school science are:
• Clinical thermometers - These are used to measure human body temperature. Their readings are commonly given in degrees Celsius or degrees Fahrenheit.
• Laboratory thermometers - These are used in science experiments to measure the temperature of liquids, gases, or solids.
2. Measuring Temperature
Clinical Thermometers
A clinical thermometer is designed to measure human body temperature. Modern clinical thermometers are often digital and operate using batteries. Depending on the type of thermometer and the instructions provided, they may be placed under the tongue, in the armpit, or in the ear. They then give a quick reading.
How Do Clinical Thermometers Work?
• Heat sensors: They measure temperature using small heat sensors inside the device.
• Sensors: Digital clinical thermometers commonly use sensors such as thermistors or thermocouples. These sensors show changes in their electrical properties when the temperature changes.
• Display & Power: The measured value is shown on a digital display, and the device is powered by a battery.
• Units: Readings are usually given in degrees Celsius, represented by °C.
• Reliability: When placed correctly against the skin or in the specified body location, a clinical thermometer provides a fast and reliable body-temperature reading.
Precautions While Using a Digital Clinical Thermometer
1. Always read the instruction manual of the thermometer before using it.
2. Wash the tip of the thermometer with soap and water before and after use, if the manufacturer's instructions allow this.
3. While washing, make sure that the digital part or display does not come into contact with water.
4. Do not hold the thermometer by its tip. Hold it from the other end.
Temperature Scales: Celsius, Fahrenheit and Kelvin
• Celsius scale - This scale is commonly used in most countries and in school experiments. Water freezes at 0 °C and boils at 100 °C at standard sea-level pressure.
• Fahrenheit scale - This scale is used in some countries. For example, 37.0 °C = 98.6 °F.
• Kelvin scale - This scale is used in science. Its unit is the kelvin, represented by K, and it is the SI unit of temperature.
To convert a temperature from Celsius to Kelvin, use the formula:
K = °C + 273.15
To convert a temperature from Kelvin to Celsius, use the formula:
°C = K - 273.15
Notes on Writing Units
• Scale names start with a capital letter: Celsius, Fahrenheit, and Kelvin.
• The word degree is written in small letters: degree Celsius and degree Fahrenheit.
• The symbols are °C, °F, and K. The degree symbol is not used with kelvin.
• Place a space between the number and the unit. For example, write 30 °C, not 30°C.
Differences Between Digital and Mercury Thermometers
• Mercury thermometers were once common. They use the expansion of mercury in a thin glass tube to show temperature.
• Mercury is toxic. A broken mercury thermometer can be hazardous and is difficult to dispose of safely.
• Digital thermometers are safer because they contain no mercury. They give quick, clear readings and are easy to read.
• Digital thermometers use electronic heat sensors and usually give readings to one or two decimal places, or to the nearest 0.1 °C.
Non-contact Thermometers
Non-contact thermometers, also called infrared thermometers, measure temperature from a short distance without touching the person or object. They detect infrared radiation emitted from the surface. During the COVID-19 pandemic, these thermometers were widely used because they reduced the risk of spreading infection.
Fever Detection Before Thermometers
• Before thermometers were widely available, people often used methods such as checking the pulse rate to detect fever. In ancient India, an increased pulse was linked to fever.
• This method is not very accurate because many other factors, such as physical activity, stress, pain, or some illnesses, can also raise the pulse rate.
• Therefore, a thermometer gives a more reliable measurement of body temperature.
Laboratory Thermometers
A laboratory thermometer is used to measure temperature in science experiments. It is different from a clinical thermometer and is designed to measure a wider range of temperatures.
Main Parts of a Laboratory Thermometer
1. Capillary tube - A long, thin glass tube through which the liquid rises or falls.
2. Bulb - A small reservoir at the bottom that contains the liquid whose expansion is measured.
3. Liquid column - The thin line of liquid inside the capillary tube. Its top indicates the temperature.
4. Celsius scale - The marked scale alongside the tube that shows the temperature reading.
5. Stem - The narrow glass part containing the capillary tube and the scale.
Laboratory thermometers usually measure temperatures from -10 °C to 110 °C. They commonly contain either alcohol, often coloured red, or mercury, which is silver and uncoloured, as the liquid.
Reading the Temperature from a Laboratory Thermometer
1. Hold the thermometer upright.
2. Look at the top of the liquid column in the capillary tube, keeping your eye directly in line with its level.
3. Read the number on the Celsius scale that matches the top of the liquid column while the bulb is still immersed in the liquid. Wait until the liquid column stops rising before taking the reading.
Precautions While Using a Laboratory Thermometer
1. Handle it with care because it is made of glass and can break easily.
2. Do not shake a laboratory thermometer. Shaking is not required.
3. Do not hold the thermometer by the bulb because the heat from your hand can change the reading.
4. Do not place the thermometer in direct sunlight because this can give an incorrect reading.
5. When measuring a liquid, keep the bulb immersed in the liquid without allowing it to touch the sides or bottom of the container.
3. Air Temperature
Weather reports in newspapers, on television, and online usually give the highest and lowest air temperatures of the day. Air temperature changes from day to day because many factors affect the weather. Temperatures usually rise towards summer and fall during winter.
Air Temperature and How We Measure It
• Air temperature tells us how hot or cold the air around us is.
• Weather stations and meteorological centres use thermometers and electronic sensors to measure air temperature.
• Air-temperature data, together with wind, humidity, and air pressure, helps meteorologists make accurate weather forecasts.
4. Key Notes
1. Temperature measures how hot or cold something is.
2. Thermometers are instruments used to measure temperature. Common types include clinical, laboratory, and non-contact or infrared thermometers.
3. Clinical thermometers are used to measure body temperature and commonly show readings in degrees Celsius.
4. Temperature scales include Celsius, Fahrenheit, and Kelvin. The SI unit of temperature is the kelvin, represented by K.
5. Measurement techniques: For an accurate clinical reading, place the thermometer correctly in the prescribed body location. For a laboratory measurement, hold the thermometer upright and read the top of the liquid column against the scale at eye level while the bulb remains immersed in the liquid.
6. Body temperature: A typical healthy adult body temperature is about 37.0 °C or 98.6 °F. Body temperature can vary with age, activity, and time of day.
7. Laboratory thermometers usually measure temperatures from -10 °C to 110 °C and may contain coloured alcohol or uncoloured mercury.
No comments:
Post a Comment