# 6.1 Temperature  (Page 4/13)

 Page 4 / 13

Furthermore, experimentation has shown that if two systems, A and B, are in thermal equilibrium with each another, and B is in thermal equilibrium with a third system C, then A is also in thermal equilibrium with C. This conclusion may seem obvious, because all three have the same temperature, but it is basic to thermodynamics. It is called the zeroth law of thermodynamics    .

## The zeroth law of thermodynamics

If two systems, A and B, are in thermal equilibrium with each other, and B is in thermal equilibrium with a third system, C, then A is also in thermal equilibrium with C.

This law was postulated in the 1930s, after the first and second laws of thermodynamics had been developed and named. It is called the zeroth law because it comes logically before the first and second laws. An example of this law in action is seen in babies in incubators: babies in incubators normally have very few clothes on, so to an observer they look as if they may not be warm enough. However, the temperature of the air, the cot, and the baby is the same, because they are in thermal equilibrium, which is accomplished by maintaining air temperature to keep the baby comfortable.

Does the temperature of a body depend on its size?

No, the system can be divided into smaller parts each of which is at the same temperature. We say that the temperature is an intensive quantity. Intensive quantities are independent of size.

## Section summary

• Temperature is the quantity measured by a thermometer.
• Temperature is related to the average kinetic energy of atoms and molecules in a system.
• Absolute zero is the temperature at which there is no molecular motion.
• There are three main temperature scales: Celsius, Fahrenheit, and Kelvin.
• Temperatures on one scale can be converted to temperatures on another scale using the following equations:
${T}_{\text{º}\text{F}}=\frac{9}{5}{T}_{\text{º}\text{C}}+\text{32}$
${T}_{\text{º}\text{C}}=\frac{5}{9}\left({T}_{\text{º}\text{F}}-\text{32}\right)$
${T}_{\text{K}}={T}_{\text{º}\text{C}}+\text{273}\text{.}\text{15}$
${T}_{\text{º}\text{C}}={T}_{\text{K}}-\text{273}\text{.}\text{15}$
• Systems are in thermal equilibrium when they have the same temperature.
• Thermal equilibrium occurs when two bodies are in contact with each other and can freely exchange energy.
• The zeroth law of thermodynamics states that when two systems, A and B, are in thermal equilibrium with each other, and B is in thermal equilibrium with a third system, C, then A is also in thermal equilibrium with C.

## Conceptual questions

What does it mean to say that two systems are in thermal equilibrium?

Give an example of a physical property that varies with temperature and describe how it is used to measure temperature.

When a cold alcohol thermometer is placed in a hot liquid, the column of alcohol goes down slightly before going up. Explain why.

If you add boiling water to a cup at room temperature, what would you expect the final equilibrium temperature of the unit to be? You will need to include the surroundings as part of the system. Consider the zeroth law of thermodynamics.

## Problems&Exercises

What is the Fahrenheit temperature of a person with a $\text{39}\text{.}0\text{º}\text{C}$ fever?

$\text{102}\text{º}\text{F}$

Frost damage to most plants occurs at temperatures of $\text{28}\text{.}0\text{º}\text{F}$ or lower. What is this temperature on the Kelvin scale?

To conserve energy, room temperatures are kept at $\text{68}\text{.}0\text{º}\text{F}$ in the winter and $\text{78}\text{.}0\text{º}\text{F}$ in the summer. What are these temperatures on the Celsius scale?

$\text{20}\text{.}0\text{º}\text{C}$ and $\text{25}\text{.}6\text{º}\text{C}$

A tungsten light bulb filament may operate at 2900 K. What is its Fahrenheit temperature? What is this on the Celsius scale?

The surface temperature of the Sun is about 5750 K. What is this temperature on the Fahrenheit scale?

$\text{9890}\text{º}\text{F}$

One of the hottest temperatures ever recorded on the surface of Earth was $\text{134}\text{º}\text{F}$ in Death Valley, CA. What is this temperature in Celsius degrees? What is this temperature in Kelvin?

(a) Suppose a cold front blows into your locale and drops the temperature by 40.0 Fahrenheit degrees. How many degrees Celsius does the temperature decrease when there is a $\text{40}\text{.}0\text{º}\text{F}$ decrease in temperature? (b) Show that any change in temperature in Fahrenheit degrees is nine-fifths the change in Celsius degrees.

(a) $\text{22}\text{.}2\text{º}\text{C}$

(b) $\begin{array}{lll}\text{Δ}T\left(\text{º}\text{F}\right)& =& {T}_{2}\left(\text{º}\text{F}\right)-{T}_{1}\left(\text{º}\text{F}\right)\\ & =& \frac{9}{5}{T}_{2}\left(\text{º}\text{C}\right)+\text{32}\text{.}0\text{º}-\left(\frac{9}{5}{T}_{1}\left(\text{º}\text{C}\right)+\text{32}\text{.}0\text{º}\right)\\ & =& \frac{9}{5}\left({T}_{2}\left(\text{º}\text{C}\right)-{T}_{1}\left(\text{º}\text{C}\right)\right)\text{}=\frac{9}{5}\text{Δ}T\left(\text{º}\text{C}\right)\end{array}$

(a) At what temperature do the Fahrenheit and Celsius scales have the same numerical value? (b) At what temperature do the Fahrenheit and Kelvin scales have the same numerical value?

current economic plans (MDGS) needs
I don't know what is happening
surajkumar
What is economic
What is the importance of study economics
Wilma
Economic is the study of how humans make decisions in face of sacristy
Wilma
economics is the study of how humans makes decision in the face of scarcity
Kpienta
economics is the study of human behaviour when faced with difficult situation example when goods and services are scarcity.
Sydney
what is Economic
what is 4ps of economic?
production place Price product
Benedict
Criticism of elasticity
what is unemployment
ohk thanks
Gyamfi
why is unemployment rapid in the country
Gyamfi
I need more explanation
Odo
what is unemployment
not working
Bethel
some one who is willing qualified to work but can't find job
jackie
Abubakar
some one who is willing to work but can't find job
Hawa
Yes true
Brian
Hawa
unemployment refers to the ability for someone who is capable and willing to work but could not find a job..
Mnoko
some one who not able to find a job
Dennis
please what is the secret of learning?
thomas
What is stock market?
explain the various types of cost curve
Short-run average fixed cost (SRAFC) Short-run average total cost (SRAC or SRATC) Short-run average variable cost (AVC or SRAVC) Short-run fixed cost (FC or SRFC) Short-run marginal cost (SRMC) Short-run total cost (SRTC)
Romy
what's economic development and growth
what do you understand by Ceteris Paribus?
the external factor will remained constant, except the price
Hasib
everything being equal
Chenwi
explain the uses of microeconomics
uses of microeconomics
Nikita
what is economic deficit
this is a situation whereby a nation's outcome or available resources are not enough to the people thereby causing scarcity
Ariel
prices of Quality demanded is equal to Quality supplied
it's quantity demand and quantity supplied that's called equilibrium
Romy
no
NABUBOLO
they deal With prices
NABUBOLO
define the elasticity
NABUBOLO
explain different types of elasticity
NABUBOLO
oops 😬 you are right you talk about quality I tell about quantity
Romy
elasticity is the measurement of the percentage change of one economic variable in response to a change in another
Romy
Cross Elasticity of Demand (XED) Income Elasticity of Demand (YED) Price Elasticity of Supply (PES)
Romy
anything else?
Romy
I need to know everything about theory of consumer behavior
Grace
Romy, what is microeconomic?
thomas
Dauda
Thomas, microeconomics is the study of how consumers, workers, and firms interact to generate outcomes in specific markets
Kieran
Dauda, economics is the study of people and choices. it is on one side the study of wealth and on the more important side, a part of the study if man
Kieran
How does one analyze a market where both demand and supply shift?
That's equilibrium market
Ramon
but an equlibrum can appear twice on the same market... both in Movement along the Demand/supply curve of shift in the Curve
Gabriel
I Mean on the same curve..
Gabriel
how can consumer surplus be calculated
Franklyn
Got questions? Join the online conversation and get instant answers!