Temperature and it's Measurement

Edwin Ogie Library

Temperature and Its Measurement

Detailed Lesson Note: Concept of temperature, thermometric properties, calibration of thermometers, temperature scales, types of thermometers, and conversion between temperature scales.

Introduction to Temperature

Temperature is a measure of the average kinetic energy of the particles in a substance. It determines the direction of heat flow between systems. Unlike heat, temperature is an intensive property and does not depend on the size of the sample.

In this lesson, we will explore the fundamental concepts of temperature and its measurement. You will learn about the thermometric properties of materials, how thermometers are calibrated, and how different temperature scales—such as Celsius and Kelvin—are used.

Concept of Temperature

Temperature quantifies the degree of hotness or coldness of a body and is directly related to the kinetic energy of its particles. Higher temperatures indicate greater kinetic energy.

Temperature is not the same as heat; heat refers to energy transfer between bodies, while temperature is a measure of the energy within a body.

Thermometric Properties

Thermometric properties are characteristics of substances that change predictably with temperature. These include:

• Thermal Expansion: The tendency of a material to change its dimensions with temperature.
• Heat Capacity: The amount of heat required to change a substance’s temperature by a given amount.
• Sensitivity: The degree to which a material's measurable property (such as volume or resistance) changes with temperature.

Materials like mercury and alcohol are commonly used in thermometers because they exhibit consistent thermal expansion and have suitable sensitivity.

Calibration of Thermometers

Calibration is the process of setting or correcting a thermometer so that its readings match known temperature standards. This is typically done by comparing the thermometer's readings at fixed reference points.

Common calibration points include:

• Freezing point of water (0°C or 273.15 K)
• Boiling point of water (100°C or 373.15 K)

Once calibrated, the thermometer can accurately measure temperature across its range.

Temperature Scales

The two most common temperature scales used in science are:

• Celsius (°C): Based on the freezing (0°C) and boiling points (100°C) of water at standard atmospheric pressure.
• Kelvin (K): The SI unit of temperature, starting at absolute zero (0 K), where no thermal energy remains. The relation is K = °C + 273.15.

Converting between Celsius and Kelvin is straightforward: simply add or subtract 273.15.

Types of Thermometers

Thermometers come in various forms, each based on different thermometric properties:

• Mercury Thermometers: Use mercury’s uniform thermal expansion.
• Alcohol Thermometers: Use colored alcohol and are suitable for very low temperatures.
• Bimetallic Thermometers: Use two metals with different expansion rates bonded together.
• Digital Thermometers: Use electronic sensors to measure temperature.
• Infrared Thermometers: Measure temperature from a distance by detecting infrared radiation.

Conversion Between Temperature Scales

Converting temperature from Celsius to Kelvin and vice versa is simple:

K = °C + 273.15

°C = K - 273.15

Other conversions (such as Fahrenheit to Celsius) exist, but this lesson focuses on the Celsius and Kelvin scales.

Summary and Key Concepts

• Temperature: A measure of the average kinetic energy of particles.
• Thermometric Properties: Characteristics such as thermal expansion and heat capacity that change with temperature.
• Calibration: Adjusting a thermometer to match standard temperature values.
• Temperature Scales: Celsius and Kelvin scales, with K = °C + 273.15.
• Types of Thermometers: Mercury, alcohol, bimetallic, digital, and infrared.

Mastery of these concepts enables accurate measurement of temperature and proper calibration of instruments.

10 Worked Examples on Temperature and Thermometry (Solutions Hidden)

Example 1: Converting Celsius to Kelvin

Question: Convert 25°C to Kelvin.

Solution:

K = 25 + 273.15 = 298.15 K.

Example 2: Converting Kelvin to Celsius

Question: Convert 310 K to Celsius.

Solution:

°C = 310 - 273.15 = 36.85°C (approximately 37°C).

Example 3: Thermometric Property Identification

Question: Why is mercury commonly used in thermometers?

Solution:

Mercury has a high coefficient of thermal expansion, a high boiling point, and remains liquid over a wide range of temperatures, making it ideal for accurate temperature measurement.

Example 4: Thermometer Calibration

Question: Explain the calibration process of a mercury thermometer using the freezing and boiling points of water.

Solution:

The thermometer is placed in an ice-water mixture, which should read 0°C. It is then placed in boiling water, which should read 100°C. Adjustments are made so that the thermometer accurately reflects these fixed points.

Example 5: Determining Sensitivity

Question: A digital sensor changes its reading by 0.5°C for a 1°C change in temperature. Explain what this tells you about its sensitivity.

Solution:

The sensor's sensitivity is moderate, as it shows a proportional change in reading. High sensitivity would result in a larger reading change for the same temperature change.

Example 6: Understanding Temperature Scales

Question: If the boiling point of water is 100°C, what is it in Kelvin?

Solution:

Boiling point in Kelvin = 100 + 273.15 = 373.15 K.

Example 7: Identifying Types of Thermometers

Question: List two types of thermometers and mention one advantage of each.

Solution:

Mercury thermometers: High accuracy and a wide operating range.
Digital thermometers: Quick readings and ease of use.

Example 8: Temperature Conversion Problem

Question: Convert 0°C to Kelvin and explain the process.

Solution:

K = °C + 273.15, so 0°C = 0 + 273.15 = 273.15 K.

Example 9: Application of Thermometric Properties

Question: Explain why bimetallic thermometers are useful in temperature measurement.

Solution:

Bimetallic thermometers consist of two metals with different expansion rates bonded together. As temperature changes, the metals expand at different rates, causing the strip to bend. This bending is used to indicate temperature.

Example 10: Real-World Calibration Application

Question: Describe a scenario where accurate thermometer calibration is critical.

Solution:

In clinical settings, accurate body temperature measurement is critical for diagnosis and treatment. Calibrated thermometers ensure that patients’ temperatures are measured accurately.

30 CBT JAMB Quiz on Temperature and Its Measurement

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