How do we convert between Celsius and Fahrenheit scales?

To convert from Celsius to Fahrenheit, use the formula: °F = (°C × 9/5) + 32. To convert from Fahrenheit to Celsius, use: °C = (°F - 32) × 5/9. These formulas account for the different zero points and unit sizes of the two scales.

How do heat pumps use temperature differences to heat or cool spaces efficiently?

Heat pumps work by moving heat from a colder area to a warmer one, which seems to violate the natural flow of heat. They achieve this by using a refrigerant cycle and compressor to absorb heat at a low temperature and release it at a higher temperature. This process can be reversed for cooling. The efficiency of heat pumps depends on the temperature difference they're working against, making them particularly effective in moderate climates.

How does temperature affect the viscosity of fluids?

For most liquids, viscosity decreases as temperature increases. This is because higher temperatures increase the kinetic energy of molecules, reducing intermolecular forces and allowing them to flow more easily. However, for gases, viscosity typically increases with temperature due to increased molecular motion. Understanding this relationship is crucial in fluid dynamics, engineering, and many industrial processes.

What is the concept of thermal noise in electronics and how does it relate to temperature?

Thermal noise, also known as Johnson-Nyquist noise, is the electronic noise generated by the thermal agitation of charge carriers in a conductor. It increases with temperature and sets a fundamental limit on the sensitivity of electronic devices. This concept is crucial in electronics, telecommunications, and the design of sensitive measurement equipment.

How does superconductivity relate to temperature?

Superconductivity is a phenomenon where certain materials lose all electrical resistance below a critical temperature. This temperature is typically very low, often near absolute zero. Understanding the relationship between superconductivity and temperature is crucial for applications in physics and engineering, such as creating powerful electromagnets or efficient power transmission systems.

What is temperature and how is it different from heat?

Temperature is a measure of the average kinetic energy of particles in a substance, indicating how hot or cold it is. Heat, on the other hand, is the transfer of thermal energy between objects due to a temperature difference. Temperature is a property of an object, while heat is energy in transit.

Why do we need different temperature scales?

Different temperature scales were developed for various historical and practical reasons. The most common scales (Celsius, Fahrenheit, and Kelvin) serve different purposes and are used in different contexts, such as everyday life, scientific research, or industrial applications.

What is the significance of absolute zero?

Absolute zero is the lowest possible temperature, where particles have the least possible thermal energy. It's significant because it represents a theoretical limit that cannot be reached in practice. At absolute zero, all molecular motion would cease, except for quantum effects.

How does the Kelvin scale relate to absolute zero?

The Kelvin scale is an absolute temperature scale that starts at absolute zero (0 K). This makes it useful for scientific calculations, as there are no negative temperatures on the Kelvin scale. Each Kelvin unit is the same size as a Celsius degree, but the scale is shifted so that 0°C = 273.15 K.

Why is the boiling point of water 100°C but 212°F?

The Celsius and Fahrenheit scales have different reference points and unit sizes. In Celsius, 0°C is the freezing point of water and 100°C is the boiling point. In Fahrenheit, these points are set at 32°F and 212°F respectively. The scales use different-sized units, resulting in different numerical values for the same temperature.

What is the difference between heat capacity and specific heat capacity?

Heat capacity is the amount of heat energy required to raise the temperature of an entire object by one degree. Specific heat capacity is the amount of heat energy required to raise the temperature of one unit mass of a substance by one degree. Specific heat capacity is a property of the material, while heat capacity depends on both the material and the amount of it.

Why does evaporation cause cooling?

Evaporation causes cooling because it requires energy. When liquid molecules with enough kinetic energy escape into the gas phase, they take this energy with them, leaving the remaining liquid with a lower average kinetic energy. This decrease in average kinetic energy is observed as a temperature drop in the remaining liquid.

What is the relationship between temperature and pressure in a closed system?

In a closed system with a fixed volume, temperature and pressure are directly proportional according to Gay-Lussac's law. As temperature increases, molecules move faster and collide more frequently with the container walls, increasing pressure. This relationship is crucial in understanding many thermodynamic processes and systems.

How does the temperature of the universe relate to its expansion?

As the universe expands, it cools. This cooling is a result of the expansion itself, as the energy density decreases with increasing volume. The temperature of the universe is closely tied to its age and size, and studying this relationship helps cosmologists understand the evolution of the universe from the hot, dense state just after the Big Bang to its current cooler, expanded state.

What is the Mpemba effect and why is it counterintuitive?

The Mpemba effect is the observation that, under certain conditions, warm water can freeze faster than cold water. This phenomenon is counterintuitive because we generally expect colder substances to reach freezing point more quickly. The effect demonstrates the complexity of freezing processes and has sparked debates and research in thermodynamics.

How do animals in extreme environments regulate their body temperature?

Animals in extreme environments use various strategies to regulate body temperature. These can include behavioral adaptations (like seeking shade or sunbathing), physiological adaptations (like sweating or shivering), and anatomical adaptations (like fur or blubber). Understanding these mechanisms provides insights into thermoregulation and has applications in fields like biology, medicine, and materials science.

What is the relationship between temperature and electrical resistance in metals?

In most metals, electrical resistance increases with temperature. This is because higher temperatures cause more atomic vibrations, which interfere with the flow of electrons. This relationship is nearly linear for many metals and is the basis for resistance thermometers. Understanding this connection is crucial in electrical engineering and materials science.

How does temperature affect the solubility of gases in liquids?

Generally, the solubility of gases in liquids decreases as temperature increases. This is because higher temperatures increase the kinetic energy of gas molecules, making it easier for them to overcome the attractive forces of the liquid and escape. This principle is important in many areas, including environmental science (e.g., dissolved oxygen in water bodies) and industrial processes.

What is the concept of color temperature in lighting and how does it relate to actual temperature?

Color temperature in lighting refers to the appearance of light from a source, measured in Kelvin (K). It's based on the color a black body radiator would emit at that temperature. However, it doesn't represent the actual temperature of the light source. For example, "warm" colors like red and orange have lower color temperatures (2700-3000K), while "cool" blues have higher color temperatures (5000K+). This concept is crucial in photography, film, and lighting design.

How does the greenhouse effect relate to temperature regulation on Earth?

The greenhouse effect is a natural process where certain gases in Earth's atmosphere trap heat, warming the planet's surface. Without it, Earth would be much colder. However, human activities increasing greenhouse gas concentrations are enhancing this effect, leading to global warming. Understanding this process is crucial for climate science and environmental policy.

What is the concept of thermal diffusivity and how does it differ from thermal conductivity?

Thermal diffusivity measures how quickly a material can change its temperature when exposed to a temperature gradient. It's the ratio of thermal conductivity to volumetric heat capacity. While thermal conductivity measures a material's ability to conduct heat, thermal diffusivity indicates how quickly it will reach thermal equilibrium. This concept is important in heat transfer analysis and materials selection.

What is the relationship between temperature and the speed of chemical reactions?

Generally, higher temperatures increase the rate of chemical reactions. This is because higher temperatures provide more kinetic energy to molecules, increasing the frequency and energy of collisions between reactant molecules. This relationship is described by the Arrhenius equation and is fundamental in chemical kinetics, affecting fields from industrial chemistry to biochemistry.

How does temperature affect the strength and properties of materials?

Temperature can significantly affect material properties. Generally, as temperature increases, materials become more ductile but less strong. This can lead to phenomena like thermal expansion, changes in crystal structure, and in extreme cases, melting or decomposition. Understanding these effects is crucial in materials science, engineering, and the design of structures and machines operating in various temperature conditions.

What is the concept of critical temperature in superconductivity and superfluidity?

The critical temperature is the temperature below which a material becomes superconducting or superfluid. For superconductors, it's the temperature at which electrical resistance disappears. For superfluids, it's the point where viscosity vanishes. These phenomena represent quantum effects becoming apparent on a macroscopic scale and are crucial in low-temperature physics and potential technological applications.

How does the human body maintain its core temperature?

The human body maintains its core temperature through a process called thermoregulation. This involves a complex system of physiological responses controlled by the hypothalamus. Methods include sweating to cool down, shivering to generate heat, and adjusting blood flow to the skin. Understanding this process is crucial in medicine, physiology, and the development of protective clothing and equipment.

What is the relationship between temperature and pressure in the atmosphere?

In the atmosphere, temperature and pressure are inversely related at a given altitude. As you go higher in the atmosphere, both temperature and pressure generally decrease. This relationship is complicated by factors like humidity and solar radiation. Understanding these atmospheric dynamics is crucial in meteorology, aviation, and climate science.

How does temperature affect the behavior of semiconductors?

Temperature significantly influences semiconductor behavior. As temperature increases, the number of charge carriers (electrons and holes) increases, affecting conductivity. However, it also increases lattice vibrations, which can impede charge flow. This complex relationship is crucial in the design and operation of electronic devices, solar cells, and thermoelectric materials.

What is the concept of thermal equilibrium in statistical mechanics?

In statistical mechanics, thermal equilibrium is a state where a system's macroscopic properties (like temperature and pressure) remain constant over time, despite ongoing microscopic fluctuations. It's characterized by the most probable distribution of energy among particles. This concept is fundamental to understanding the connection between microscopic particle behavior and macroscopic thermodynamic properties.

How do animals like desert lizards use behavioral thermoregulation?

Desert lizards use behavioral thermoregulation to maintain their body temperature in extreme environments. This includes basking in the sun to warm up, seeking shade to cool down, and changing body posture to adjust exposure to the sun. By actively managing their exposure to heat sources and sinks, they can maintain optimal body temperatures for survival and activity.

What is the concept of effective temperature in astrophysics?

Effective temperature in astrophysics is

Can temperature ever be negative?

On the Celsius and Fahrenheit scales, negative temperatures are possible and common. However, on the Kelvin scale, which is based on absolute zero, negative temperatures are not possible. Negative temperatures on Celsius and Fahrenheit scales simply indicate temperatures below their respective zero points.

How does altitude affect the boiling point of water?

As altitude increases, atmospheric pressure decreases. This lower pressure allows water molecules to escape more easily, reducing the boiling point. For example, water boils at 100°C at sea level, but at about 93°C on Mount Everest due to the lower atmospheric pressure at high altitudes.

What is the triple point of water and why is it important?

The triple point of water is the unique combination of temperature and pressure at which water can exist simultaneously as a solid, liquid, and gas in equilibrium. It occurs at 273.16 K (0.01°C) and a pressure of 611.73 Pa. This point is important as a fixed reference for calibrating thermometers and defining the Kelvin scale.

Why is the Kelvin scale preferred in scientific calculations?

The Kelvin scale is preferred in scientific calculations because it's an absolute scale starting at absolute zero, eliminating negative values. This makes mathematical operations simpler and more consistent, especially in thermodynamics and statistical mechanics where absolute temperature is often required.

How do thermocouples work and why are they useful for measuring high temperatures?

Thermocouples work based on the thermoelectric effect: when two different metals are joined, a voltage is produced that depends on the temperature difference between the junction and the reference point. Thermocouples are useful for measuring high temperatures because they can withstand extreme conditions, have a wide temperature range, and respond quickly to temperature changes.

What is the concept of thermal radiation and how does it relate to temperature?

Thermal radiation is electromagnetic radiation emitted by all objects above absolute zero temperature. The intensity and wavelength of this radiation depend on the object's temperature. Hotter objects emit more intense radiation at shorter wavelengths. This principle is used in technologies like infrared cameras and is crucial in understanding heat transfer and the behavior of stars.

Temperature And Its Scales

Physics
Mechanical Properties of Fluids
Temperature And Its Scales

Temperature And Its Scales

Vishal kumarUpdated on 02 Jul 2025, 07:59 PM IST

Temperature is a fundamental concept in science that measures how hot or cold an object is. It's an essential part of everyday life, influencing everything from the clothes we wear to how we cook food. For instance, we check the temperature to decide if we need a jacket or to ensure the oven is set right for baking a cake. Temperature also plays a crucial role in technology and health, from monitoring weather forecasts to measuring body temperature during illness. There are different scales to measure temperature, such as Celsius, Fahrenheit, and Kelvin, each suited to specific fields. For example, while Celsius is common in daily life, scientists often use Kelvin for precise calculations. Understanding temperature scales helps us navigate both everyday tasks and scientific explorations.

This Story also Contains

Temperature And Its Scales
Solved Examples Based On Temperature And Its Scales
Summary

Temperature And Its Scales

Temperature is a measure of the degree of heat present in an object or environment, affecting the behaviour of substances in everyday life and in scientific contexts. It helps us determine whether something is hot or cold, guiding our decisions from adjusting air conditioners to setting oven temperatures while cooking. Temperature is also critical in various industries, such as refrigeration, metallurgy, and healthcare, where precise control is essential. To quantify temperature, different scales are used globally, including Celsius, Fahrenheit, and Kelvin. Each scale serves distinct purposes: Celsius is commonly used in most countries for daily temperature measurement, Fahrenheit is mainly used in the United States, and Kelvin is the standard in scientific research, particularly in understanding absolute temperatures.

Let's discuss one by one

Temperature

Temperature is the degree of hotness or coldness of a body. Heat always flows from high temperature to low temperature if no external work is applied.

Temperature is one of the seven fundamental quantities and its dimension is $[\theta]$. S.I. unit of temperature is Kelvin.

Scales of Temperature

To construct any scale of temperature, we have to take two fixed points. The first fixed point is the freezing point (ice point) of water. The second fixed point is the boiling point (steam point) of water.

Celsius scale: In this scale, the ice point is taken at 0° and the steam point is taken at 100°. The temperature measured on this scale is all in degrees Celsius(°C).

Fahrenheit scale: This scale of temperature has a freezing point of 32°F and a steam point of 212°F.

Kelvin scale: The Kelvin temperature scale is also known as the thermodynamic scale. The temperature measured on this scale is in Kelvin (K).

Note - The triple point of water is also selected to be the zero of the scale of temperature

The temperature on any scale can be converted into any other scale by using the following formula

$\frac{(\text { Reading on any scale }- \text { Ice point })}{(\text { Steam point }- \text { ice point })}$

All the above-mentioned temperature scales are related to each other by the following relationship

$\frac{C}{5}=\frac{F-32}{9}=\frac{K-273}{5}$

The table below shows the range of various temperature scales

Solved Examples Based On Temperature And Its Scales

Example 1: The graph between two temperature scales $P$ and $Q$ is shown in the figure. Between the upper fixed point and the lower fixed point, there are 150 equal divisions of scale $P$ and 100 divisions on scale $Q$. The relationship for conversion between the two scales is given by:-

1) $\frac{t_p}{100}=\frac{t_Q-180}{150}$
2) $\frac{t_Q}{150}=\frac{t_P-180}{100}$
3) $\frac{t_p}{180}-\frac{t_Q-40}{100}$
4) $\frac{t_Q}{100}=\frac{t_P-30}{150}$

Solution

$\begin{aligned} & \frac{t_p-30}{180-30}=\frac{t_Q-0}{100-0} \\ & \frac{t_p-30}{150}=\frac{t_Q}{100} \\ & \frac{t_Q}{100}=\frac{t_p-30}{150}\end{aligned}$

Hence, the answer is the option (4).

Example 2: On a temperature scale ' X ', the boiling point of water is $65^0 \mathrm{X}$ and the freezing point is $-15^0 \mathrm{X}$. Assume that the X scale is linear. The equivalent temperature corresponding to the Fahrenheit scale would be :

1) $-63^0 \mathrm{~F}$
2) $-148^0 \mathrm{~F}$
3) $-48^0 \mathrm{~F}$
4) $-112^0 \mathrm{~F}$

Solution:

$\begin{aligned} & \frac{X_T-X_L}{X_H-X_L}=\frac{T_F-32}{212-32} \\ & \frac{-95^{\circ}-\left(-15^{\circ}\right)}{65^{\circ}-\left(-15^{\circ}\right)}=\frac{T_F-32}{180} \\ & \frac{-80^{\circ}}{80^{\circ}}=\frac{T_F-32}{180^{\circ}} \\ & -180=T_F-32 \\ & T_F=-180+32=-148^{\circ} \mathrm{F}\end{aligned}$

Hence, the answer is the option (2).

Example 3: On linear temperature scale Y, water freezes at 160^o Y and boils at - 50^o Y. On this Y scale, a temperature of 340 K would be read as : ( water freezes at 273 K and boils at 373 K )

1) $-73.7^{\circ} Y$
2) $-233.7^{\circ} \mathrm{Y}$
3) $-86.3^{\circ} \mathrm{Y}$
4) $-106.3^{\circ} Y$

Solution:

Since the temperature scale is assumed to be linear, the slope in the two cases will be the same. Hence,
$\begin{aligned} & \frac{Y-(-160)}{-50-(-160)}=\frac{K-273}{373-273} \\ & \frac{Y+160}{110}=\frac{K-273}{100} \\ & Y=\frac{11}{10}(K-273)-160 \\ & Y=\frac{11}{10}(340-273)-160=-86.3^0 Y\end{aligned}$

Hence, the answer is the option (3).

Example 4: The graph PQ shown in the figure is a plot of the temperature of a body in degrees Celsius and degrees Fahrenheit. Then, the slope of line PQ is

1) $\frac{3}{5}$
2) $\frac{5}{3}$
3) $\frac{9}{5}$
4) $\frac{5}{9}$

Solution:

Slope of PQ

$\begin{aligned} & =\frac{y_2-y_1}{x_2-x_1} \\ & =\frac{100-0}{212-32} \\ & =\frac{100}{180}=\frac{5}{9}\end{aligned}$

Hence, the answer is the option (4).

Example 5: What is the value of $-196^{\circ} \mathrm{C}$ in the Kelvin scale

1) 87

2) 77

3) 107

4) 117

Solution:

Kelvin Scale

The Kelvin temperature scale is also known as the thermodynamic scale.

wherein

The temperature measured on this scale is in Kelvin(K).

$\begin{aligned} & T_k=273+T_C \\ & =273+(-196 C) \\ & T_k=77 \text { Kelvin }\end{aligned}$

Hence, the answer is the option (2).

Summary

Temperature is a measure of the average kinetic energy of the particles in a substance; it indicates if a substance is hot or not. It has several temperature scales though, the most commonly used being Celsius, Fahrenheit, and Kelvin. Celsius is the one mainly used by the majority worldwide and is defined as it states that 0°C represents the freezing point and 100°C the boiling point. Fahrenheit is used mainly in the USA, and it defines the freezing point of water at 32°F and the boiling point at 212°F. Kelvin is used mainly for scientific purposes, whose zero point thermodynamically corresponds to absolute zero—the point at which the particles are in minimum thermal motion—but has a gradation like Celsius, so the freezing point of water is 273.15 K and the boiling point is 373.15 K. These scales allow us to do much, from the simplest use in weather forecasting to high-end scientific research applications to purposes in our lives.

Frequently Asked Questions (FAQs)

Q: How do quantum effects influence temperature measurements at extremely low temperatures?

At extremely low temperatures, near absolute zero, quantum effects become significant. Classical thermodynamics breaks down, and phenomena like quantum tunneling and zero-point energy become important. This affects temperature measurements and the very definition of temperature. Understanding these effects is crucial in low-temperature physics, quantum computing, and the study of exotic states of matter.

Q: What is the concept of negative absolute temperature and how is it possible?

Negative absolute temperature is a concept that can occur in systems with a limited number of energy states, such as certain spin systems. It doesn't mean temperatures below absolute zero, but rather a state where higher energy states are more populated than lower ones. This concept challenges our usual understanding of temperature and has implications in quantum physics and thermodynamics.

Q: How does temperature affect the speed of sound in different media?

The speed of sound generally increases with temperature in most media. In gases, higher temperatures lead to faster molecular motion, allowing sound waves to propagate more quickly. In liquids and solids, increased temperature usually results in decreased density and/or increased elasticity, both of which can increase sound speed. This relationship is important in acoustics and meteorology.

Q: What is the relationship between temperature and phase transitions?

Temperature plays a crucial role in phase transitions. At specific temperatures (at a given pressure), substances undergo transitions between solid, liquid, and gas phases. These transition temperatures (melting point, boiling point) are characteristic of each substance. Understanding this relationship is essential in materials science, chemistry, and many industrial processes.

Q: What is the concept of thermal inertia and how does it affect temperature measurements?

Thermal inertia is the resistance of a material or system to temperature change. Materials with high thermal inertia take longer to heat up or cool down. This affects temperature measurements because it influences how quickly a thermometer can reach thermal equilibrium with its surroundings, potentially leading to delayed or inaccurate readings if not accounted for.

Q: How does the expansion of mercury in a thermometer relate to temperature measurement?

Mercury expands uniformly with increasing temperature. In a mercury thermometer, this expansion causes the mercury to rise in a narrow glass tube. The height of the mercury column corresponds to specific temperatures, which are marked on the thermometer's scale. This linear relationship between volume and temperature makes mercury useful for accurate temperature measurements.

Q: What is thermal equilibrium and why is it important in temperature measurement?

Thermal equilibrium is the state where two or more objects in thermal contact have reached the same temperature, with no net heat transfer between them. It's crucial in temperature measurement because a thermometer must reach thermal equilibrium with the object or environment it's measuring to provide an accurate reading.

Q: How do digital thermometers work compared to traditional liquid-in-glass thermometers?

Digital thermometers typically use electronic sensors (like thermistors or thermocouples) that change their electrical properties with temperature. These changes are converted into a digital readout. Unlike liquid-in-glass thermometers, which rely on thermal expansion, digital thermometers can provide faster, more precise readings and can measure a wider range of temperatures.

Q: How does the concept of temperature relate to the kinetic theory of gases?

According to the kinetic theory of gases, temperature is directly related to the average kinetic energy of gas molecules. Higher temperatures correspond to faster-moving molecules with higher kinetic energies. This molecular-level understanding helps explain macroscopic properties of gases and their behavior under different conditions.

Q: What is the difference between intensive and extensive properties, and how does temperature fit in?

Intensive properties do not depend on the amount of substance present, while extensive properties do. Temperature is an intensive property because it doesn't change with the amount of substance. For example, half a liter of water at 50°C has the same temperature as a full liter at 50°C, even though the total heat content (an extensive property) is different.

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