18.3
Termômetros e Escalas de Temperatura
Qualquer propriedade física que dependa consistentemente, e de forma reprodutível, da temperatura pode ser usada como base para um termômetro. Por exe…
Um termômetro é um dispositivo usado para medir a temperatura de um corpo ou objeto.
Alguns dos tipos mais importantes de termômetros são termômetros líquidos em vidro, bimetálicos, digitais, infravermelhos e gasosos.
Os termômetros medem a temperatura em três escalas principais: Celsius, Fahrenheit e Kelvin. Essas balanças foram projetadas com base nos pontos de congelamento e ebulição da água.
Na escala de temperatura Celsius, o ponto de congelamento da água é rotulado como zero, enquanto o ponto de ebulição da água é rotulado como cem. Existem intervalos de cem graus entre esses dois pontos, razão pela qual também é conhecida como escala centígrada.
Aqui, a unidade de temperatura é grau Celsius.
Na escala de temperatura Fahrenheit, o ponto de congelamento da água é indicado em 32, enquanto o ponto de ebulição é 212. A unidade de temperatura nesta escala é o grau Fahrenheit.
A temperatura na escala Fahrenheit pode ser facilmente convertida em Celsius empregando a equação de conversão.
A escala de temperatura Kelvin é uma escala de temperatura absoluta. Aqui, zero kelvin indica zero absoluto, que é a temperatura mais baixa possível.
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Q1: What are the main types of thermometers used to measure temperature?
The most important thermometer types include liquid-in-glass, bimetallic, digital, infrared, and gas thermometers. Liquid-in-glass thermometers use alcohol or mercury that expands with temperature. Infrared thermometers measure radiation emission and are commonly used for body temperature measurement in the ear canal, offering greater accuracy than traditional methods.
Q2: How do alcohol thermometers work to measure temperature changes?
Alcohol thermometers rely on thermal expansion, where the liquid expands more rapidly than the glass encasing it. When temperature increases, alcohol from the bulb is forced into a narrow tube, producing a large visible change in column length for small temperature changes. This design amplifies the temperature signal for easy reading.
Q3: What is the difference between Celsius and Fahrenheit temperature scales?
On the Celsius scale, water freezes at 0 degrees and boils at 100 degrees, creating 100 equal intervals also called centigrade. On the Fahrenheit scale, water freezes at 32 degrees and boils at 212 degrees. Temperature can be converted between these scales using a mathematical conversion equation.
Q4: What does absolute zero represent on the Kelvin temperature scale?
The Kelvin scale is an absolute temperature scale where zero kelvin represents absolute zero, the lowest possible temperature. Unlike Celsius and Fahrenheit, which use arbitrary reference points based on water's freezing and boiling points, the Kelvin scale is grounded in fundamental physical principles and is essential for scientific calculations.
Q5: How are temperature scales created and standardized?
Temperature scales are created by identifying two reproducible reference temperatures, typically the freezing and boiling points of water at standard atmospheric pressure. These fixed points establish the scale's range and intervals. All three common scales—Fahrenheit, Celsius, and Kelvin—use this principle to ensure consistent, reliable temperature measurement across different thermometer types.
Q6: What physical properties can be used as the basis for thermometer design?
Any physical property that depends consistently and reproducibly on temperature can form a thermometer's basis. Common properties include volume expansion in liquids, electrical resistance, color changes, and infrared radiation emission. This variety of measurable properties explains why so many different thermometer types exist for specialized applications.
Q7: Why are infrared thermometers more accurate for measuring body temperature?
Infrared thermometers measure radiation emission, which varies predictably with temperature, providing rapid and accurate readings. When placed in the ear canal, they detect infrared radiation directly from the tympanum, avoiding contact errors. This method is more accurate than traditional alcohol thermometers placed under the tongue or armpit, which depend on thermal contact and can be affected by placement variations.