THERMODYNAMICS: Temperature

Temperature expresses the hotness or coldness of a body, it is one of the seven SI base quantities. The equipment used to measure temperature is called thermometer.
Physicists measure temperature on the Kelvin scale, which is marked in units called kelvins. Kelvin scale is an Absolute scale It is expected to have no negative value and Kelvin scale doesn't have degrees unlike Celsius and Fahrenheit temperature scales.

Nearly all of the other countries in the world uses Celsius scale or formerly known as centigrade scale while United States uses Fahrenheit scale.

Temperature of a body has no upper limit but it does have a lower limit, This lower limit is called the Absolute zero and it is taken as the zero of the Kelvin.

Here, We have the comparisons of the different Temperature scales.

Since, We have different temperature scales we should learn how to convert from one scale to another.

Kelvin to Celsius:

Celsius to Fahrenheit:

Examples:
1. Aluminum metal melts at 660.37 C. What is the temperature in Kelvin?

2. The title of the book "Fahrenheit 451" refers to the temperature that book paper burns, or 451 F. What is the temperature in Celsius?

3. Room temperature is often used in calculations as 300 K. What is the temperature in Fahrenheit?

Temperature as measure of kinetic energy

Another definition of Temperature is a measure of how much kinetic energy - that is, energy in motion is in a system. The hotter the system is, It has more kinetic energy because it's atoms and molecules moving around.

Let's watch this little experiment to visualize the above definition:

The average kinetic energy of the particles is directly related to the temperature of the object by the following equation:

Examples:

1. Given that the average kinetic energy of the particles comprising our sun is 1.2×10^-19J, find the temperature of the sun.

The easiest way to figure out if there is a difference in temperature between two systems is through heat transfer "The hotter system will always transfer heat to the colder one. And if there is no heat transfer in a system at all, It is called Thermal Equilibrium.

But normally there will be some Heat transfer because that is how temperature of a system change. When temperature of a system changes it will undergo "thermal expansion" An increase in temperature can make solid expands and a decrease in temperature make it contracts. There are two ways on how a dimension of a solid may change it can decrease or increase in length(1-dimensional) or it can decrease or increase in volume(3 Dimensional).

Thermal Expansion

The properties of many bodies change as we alter their temperature, perhaps by moving them from refrigerator to a warm oven.

To give a few examples: As their temperature increases, the volume of a liquid increases, a metal rod grows a little longer, and the electrical resistance of a wire increases, as does the pressure exerted by a confined gas.

Let's watch these two struggle opening the pickle jar...

See? even "Mr. Big guy" at the GIF can't open the pickle Jar! Maybe because they skipped Thermodynamics class!

but kidding aside, you can often loosen a tight metal jar lid by holding it under a stream of hot water both the metal of the lid and the glass of the jar expand as the hot water adds energy to their atoms.(With the added energy, the atoms can move a bit farther from one another than usual, against the spring-like interatomic forces that hold every solid together.) However, because the atoms in the metal move farther apart than those in the glass, the lid expands more than the jar thus is loosened.

Linear Expansion

If the temperature of a metal rod of length L is raised by an amount ΔT, its length is found to increase by an amount

Volume Expansion

If the temperature of a solid or liquid whose volume is V is increased by an amount ΔT, the increase in volume is found to be:

The coefficients of volume expansion and linear expansion for a solid are related by:

Examples:

1. An aluminum rod has a length of exactly one meter at 300K. How much longer is it when placed in a 400°C oven? when coefficient of linear expansion of aluminum is 23x10^-6 per Kelvin.

2. A glass of water with volume 1 liter is completely filled at 5°C. How much water will spill out of the glass when the temperature is raised to 85°C?when coefficient of volume expansion of water is 207x10^-6 per °Celsius. and 27x10^-6 per °Celsius for the glass.