Back to homePhysics and Chemistry · 3rd ESO · Change subject
Start for free
ESO Y3 · Physics and Chemistry
Energy · Heat and temperature

Temperature scales

The weather forecast in Spain gives the temperature in degrees Celsius. In the United States, in degrees Fahrenheit. In a physics laboratory, in kelvin. It is the same quantity — how hot or cold something is — measured with three different rulers. Knowing how to convert from one to another is as useful as knowing that a kilometre is 1000 metres.

Before you start, make sure you know: Temperature and heat (2nd ESO)
Before you start, make sure you know: First-degree equations (2nd ESO)

The three temperature scales

You dip a thermometer into a glass of water with crushed ice and it reads $0$, but in the United States it would read $32$ and in a physics laboratory they would record $273$: how can the same phenomenon be measured with three such different values?

Comparison of the freezing and boiling points of water on the Celsius, Kelvin and Fahrenheit scales: 0 and 100 °C, 273 and 373 K, 32 and 212 °F. Boiling of water Freezing of water °C 100 0 K 373 273 °F 212 32 All three mark the boiling and freezing of water with different numbers
Practice★☆☆
In Spain, the weather forecast gives the temperature in degrees Celsius, but a friend from the United States gives it to you in degrees Fahrenheit. What is a temperature…

In Spain, the weather forecast gives the temperature in degrees Celsius, but a friend from the United States gives it to you in degrees Fahrenheit. What is a temperature scale? Name the three scales you know and write the unit symbol for each.

Solve
Practice★☆☆
What is the International System unit for temperature, used in science? And which one do we use in daily life in Spain? Give an example of each.

What is the International System unit for temperature, used in science? And which one do we use in daily life in Spain? Give an example of each.

Solve

From Celsius to Kelvin

Comparison between the Celsius and Kelvin scales showing that both share the same degree size but have their starting point shifted by 273 units. °CK 0 °C 273 K 100 °C 373 K +100 +273 at every point: the gap between them (100 degrees) is the same on both scales
Practice★☆☆
On a spring day in Seville, the thermometer reads $25\ ^\circ\text{C}$. Express this temperature in kelvins, remembering that $T_K = t_C + 273$.

On a spring day in Seville, the thermometer reads $25\ ^\circ\text{C}$. Express this temperature in kelvins, remembering that $T_K = t_C + 273$.

Solve
Practice★☆☆
At what temperature, in degrees Celsius, does water freeze? And at what temperature does it boil at sea level? Express both values in kelvins as well.

At what temperature, in degrees Celsius, does water freeze? And at what temperature does it boil at sea level? Express both values in kelvins as well.

Solve
Practice★★☆
During a heatwave in Córdoba, temperatures reach $44\ ^\circ\text{C}$. a) Express this temperature in kelvins. b) How many kelvins difference is there compared to normal…

During a heatwave in Córdoba, temperatures reach $44\ ^\circ\text{C}$.

  1. a) Express this temperature in kelvins.
  2. b) How many kelvins difference is there compared to normal body temperature, $37\ ^\circ\text{C}$?
Solve

Degrees Fahrenheit

You are reading an American baking recipe and it says to preheat the oven to $350\ ^\circ\text{F}$, a figure that would burn your food to a cinder if these were our units: how many degrees Celsius is that temperature really?

Two identical thermometers, one with a Celsius scale and the other with a Fahrenheit scale. The freezing point of water is at 0 °C and 32 °F, and the boiling point at 100 °C and 212 °F. Between the two fixed points there are 100 degrees Celsius and 180 degrees Fahrenheit, so 50 °C coincides with 122 °F. The two thermometers show the same temperature: 20 °C is equivalent to 68 °F. Celsius (°C) Fahrenheit (°F) 0 50 100 32 122 212 boiling point of water freezing point of water 20 °C = 68 °F 100 degrees 180 degrees between the fixed points: 100 °C is equivalent to 180 °F → 180/100 = 1,8
Practice★☆☆
The classroom temperature is $20\ ^\circ\text{C}$. Calculate what this is in degrees Fahrenheit using the expression $T_F = 1,8 \cdot t_C + 32$.

The classroom temperature is $20\ ^\circ\text{C}$. Calculate what this is in degrees Fahrenheit using the expression $T_F = 1,8 \cdot t_C + 32$.

Solve
Practice★★☆
A kitchen thermometer bought in the United States reads $122\ ^\circ\text{F}$. Calculate the temperature in degrees Celsius by rearranging the expression…

A kitchen thermometer bought in the United States reads $122\ ^\circ\text{F}$. Calculate the temperature in degrees Celsius by rearranging the expression $T_F = 1,8 \cdot t_C + 32$.

Solve
Practice★★☆
An American biscuit recipe says to bake at $392\ ^\circ\text{F}$. a) Convert this temperature to degrees Celsius. b) Then express it in kelvins.

An American biscuit recipe says to bake at $392\ ^\circ\text{F}$.

  1. a) Convert this temperature to degrees Celsius.
  2. b) Then express it in kelvins.
Solve

Absolute zero

Thermometer with the Kelvin and Celsius scales: 373 K is 100 °C, 273 K is 0 °C and absolute zero, 0 K or −273 °C, is the lower limit that cannot be passed. 373 K · 100 °C 273 K · 0 °C 0 K · −273 °C boiling point of water freezing point of water absolute zero: lower limit cannot go any lower the Kelvin scale never goes below 0: there is no "below absolute zero"
Practice★☆☆
Zero on the Kelvin scale is called absolute zero. How many degrees Celsius does it correspond to? Why do you think it is called this?

Zero on the Kelvin scale is called absolute zero. How many degrees Celsius does it correspond to? Why do you think it is called this?

Solve
Practice★★★
In Yakutsk (Siberia), temperatures as low as $-50\ ^\circ\text{C}$ have been measured. Look at the thermometer scale in the diagram: a) Express this temperature in…

In Yakutsk (Siberia), temperatures as low as $-50\ ^\circ\text{C}$ have been measured. Look at the thermometer scale in the diagram:

°C 100 50 0 −50 −100 −150 −200 −250 −50 °C Yakutsk 0 K = −273 °C absolute zero −300 °C ?
  1. a) Express this temperature in kelvins.
  2. b) Could a temperature of $-300\ ^\circ\text{C}$ ever be measured anywhere in the universe? Justify your answer using the concept of absolute zero.
  3. c) Can there be negative temperatures on the Celsius scale? And on the Kelvin scale? Give reasons for both answers.
Solve

Comparing and ordering temperatures

Two glasses of water, one at 300 K and the other at 30 °C, next to a thermometer with a kelvin scale on the left and a Celsius scale on the right: 30 °C coincides with 303 K, which is above 300 K. 300 K 30 °C K °C 303 300 30 27 30 °C = 303 K > 300 K
Practice★★☆
Which is hotter: a glass of water at $300\ \text{K}$ or a glass of water at $30\ ^\circ\text{C}$? Convert both values to the same scale before comparing.

Which is hotter: a glass of water at $300\ \text{K}$ or a glass of water at $30\ ^\circ\text{C}$? Convert both values to the same scale before comparing.

Solve
Practice★★☆
Order the following temperatures from lowest to highest, first expressing them all in degrees Celsius: a) $50\ ^\circ\text{F}$ b) $280\ \text{K}$ c) $0\ ^\circ\text{C}$

Order the following temperatures from lowest to highest, first expressing them all in degrees Celsius:

  1. a) $50\ ^\circ\text{F}$
  2. b) $280\ \text{K}$
  3. c) $0\ ^\circ\text{C}$
Solve
Practice★★★
We want to know what a temperature increase of $10\ ^\circ\text{C}$ is equivalent to on the other scales. a) Express $20\ ^\circ\text{C}$ and $30\ ^\circ\text{C}$ in…

We want to know what a temperature increase of $10\ ^\circ\text{C}$ is equivalent to on the other scales.

  1. a) Express $20\ ^\circ\text{C}$ and $30\ ^\circ\text{C}$ in kelvins and in degrees Fahrenheit.
  2. b) Calculate the difference between both values on each of the three scales.
  3. c) Conclude which two scales have degrees of the same size and which scale has the smallest degrees.
Solve

Summary

Let's practice! 8 medium exercises in this section
★★☆ A kitchen thermometer bought in the United States reads $122\ ^\circ\text{F}$. Calculate…★★☆ On a trip to Miami, Yasmin feels unwell and the chemist's thermometer reads…★★☆ Which is hotter: a glass of water at $300\ \text{K}$ or a glass of water at…
Let's practice! 8 hard exercises in this section
★★★ There is a temperature at which a Celsius thermometer and a Fahrenheit thermometer show…★★★ Liquid nitrogen, widely used in laboratories and modernist cuisine, boils at…
See all the exercises in this section