18.3
Termómetros y escalas de temperatura
Cualquier propiedad física que dependa de manera consistente y reproducible de la temperatura puede ser utilizada como base de un termómetro. Por ejem…
Un termómetro es un dispositivo que se utiliza para medir la temperatura de un cuerpo u objeto.
Algunos de los tipos de termómetros más importantes son los termómetros de líquido en vidrio, bimetálicos, digitales, infrarrojos y de gas.
Los termómetros miden la temperatura en tres escalas principales: Celsius, Fahrenheit y Kelvin. Estas escalas se diseñaron en función de los puntos de congelación y ebullición del agua.
En la escala de temperatura Celsius, el punto de congelación del agua está etiquetado como cero, mientras que el punto de ebullición del agua está etiquetado como cien. Hay intervalos de cien grados entre estos dos puntos, por lo que también se conoce como escala centígrada.
Aquí, la unidad de temperatura es el grado Celsius.
En la escala de temperatura Fahrenheit, el punto de congelación del agua se indica en 32, mientras que el punto de ebullición es 212. La unidad de temperatura en esta escala es el grado Fahrenheit.
La temperatura en la escala Fahrenheit se puede convertir fácilmente a Celsius empleando la ecuación de conversión.
La escala de temperatura Kelvin es una escala de temperatura absoluta. Aquí, cero kelvin indica el cero absoluto, que es la temperatura más baja posible.
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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.