50 Fun Facts About Heat

What is the SI unit of measurement for heat?

Heat is a process quantity: a system does not 'contain' it, it transfers it.

The SI unit of energy is named after which English physicist, a brewer's son?

He lived from 1818 to 1889 and was the son of a wealthy Salford brewer.

How many joules is one thermochemical calorie now defined to equal?

The 'large' calorie on food labels is a kilocalorie, 4,184 J.

Who first introduced the calorie as a unit of heat energy, in lectures in 1819–1824?

The lectures were on experimental calorimetry.

How many joules raise the temperature of 1 kg of water by 1 K?

Water has one of the highest specific heat capacities of any common substance.

Which heat-transfer mechanism works by warmer, less dense fluid rising and cooler fluid sinking?

It applies to liquids and gases alike, from a saucepan to the atmosphere.

Which mechanism is the diffusion of heat within a material or between materials in contact?

In metals it is dominated by free electrons; in diamond, by lattice vibrations.

Above roughly what temperature does thermal radiation become visible as a glow?

That visible glow is called incandescence; at room temperature emission is mostly infrared.

Which allotropes of carbon are credited with the highest thermal conductivities at room temperature?

Diamond conducts heat via lattice vibrations rather than free electrons.

Who introduced the term 'latent heat' around 1750, commissioned by Scotch whisky producers?

The distillers wanted the ideal quantities of fuel and water for their stills.

What is absolute zero on the Celsius scale?

It equals 0 K and −459.67 °F.

Which French physicist first asked in 1703 whether there is a limit to coldness?

The question arose from his improvements to the air thermometer.

Which scales set their zero points at absolute zero by definition?

Rankine uses Fahrenheit-sized degrees; Kelvin uses Celsius-sized ones.

In which year did William Thomson publish 'On an Absolute Thermometric Scale'?

He was later ennobled as Lord Kelvin.

When the kelvin joined the SI in 1954, 273.16 K was defined as the temperature of what?

The 2019 SI revision instead fixed the Boltzmann constant.

In which year was 'degree Kelvin' (°K) renamed simply 'kelvin' (K)?

Resolution 3 of the 13th CGPM made the change.

Anders Celsius's original 1742 scale set which value at the boiling point of water?

His scale ran upside-down, with 100 at freezing; it was reversed after his death.

Which Swedish botanist reversed Celsius's scale in 1744 to the form used today?

The change coincided with Anders Celsius's death.

What was the profession of Anders Celsius, after whom the scale is named?

The scale was long called centigrade, from the Latin for 100 steps.

Fahrenheit's 0 °F was set as the freezing point of a brine of water, ice and which salt?

A German story says he chose the coldest winter air temperature in Danzig in 1708–09 and only later reproduced it with brine.

How many Fahrenheit degrees separate water's freezing and boiling points?

Freezing was defined as 32 °F and boiling as 212 °F at standard pressure.

Fahrenheit's upper fixed point, average human body temperature, was finally set at what?

He had originally set it at 90 °F.

In 1714 Daniel Gabriel Fahrenheit built a reliable thermometer using which liquid?

Earlier devices had used alcohol and water mixtures.

Galileo and Santorio Santorio built early temperature devices with an air-filled what?

The bulb connected to a tube partially filled with water.

A bimetallic-strip thermometer bends because of differing what between two metals?

The same principle once switched older home thermostats on and off.

James Joule's father ran what kind of business in Salford?

Joule later managed it and around 1840 began investigating replacing its steam engines with electric motors.

Who observed heat from boring cannon in Munich and reported on it in 1798?

Born Benjamin Thompson, he immersed a cannon barrel in water with a blunted boring tool to make it boil.

Which chemist introduced a version of the caloric theory, treating heat as a fluid?

Rumford's cannon experiments were an early blow against it.

Benjamin Thompson, the cannon-boring count, also laid out which Munich park in 1789?

It remains one of the largest urban public parks in the world.

Who invented the vacuum flask, or thermos, in 1892?

It is two flasks, one inside the other, joined at the neck with a vacuum between them.

What is the official highest air temperature ever recorded on Earth?

It was measured at Furnace Creek Ranch, Death Valley, on July 10, 1913.

A 1922 reading from which country held the heat record for 90 years before being decertified in 2012?

Investigators found a variety of evidence that it was inaccurate.

The air around a lightning flash heats rapidly to roughly what temperature?

The shock wave from those suddenly heated gases is what we hear as thunder.

What is the temperature at the centre of the Sun's core?

The core is the hottest part of the Solar System, at a density of 150 g/cm³.

Which engineer's pocket candy bar, melted by a radar set, led to the microwave oven?

He worked at Raytheon, which sold the first commercial model in 1947.

What was the name of Raytheon's first commercial microwave oven, sold from 1947?

Percy Spencer is generally credited with developing and patenting it.

The effect in which a water droplet skitters across a very hot pan is named after which German doctor?

He described it in A Tract About Some Qualities of Common Water.

At the summit of Mount Everest, water boils at roughly what temperature?

Air pressure there is only about 34 kPa.

Body temperature above what level counts as severe hyperthermia, a medical emergency?

It requires immediate treatment to prevent disability or death.

The heat index combines air temperature with which other measurement?

Humidity makes heat feel worse because sweat evaporates less effectively.

Who proposed the existence of the greenhouse effect as early as 1824?

He did not give it that name.

Western saunas originated in which country?

The oldest were pits dug into slopes and used as winter dwellings.

What Finnish word names the steam and heat of a sauna together?

The kiuas is the pile of heated rocks; the Estonian equivalent is leili.

The symbol Q for heat was introduced by Macquorn Rankine and which German physicist?

Both were founders of thermodynamics in the mid-19th century.

Which law gives the radiant intensity emitted by a hot body?

Wien's displacement law gives the most likely frequency of the radiation.

What did the 2019 revision of the SI fix to define the kelvin?

Each 1 K change now corresponds to an exact change in thermal energy kT.

Which of these is NOT a standard mechanism of heat transfer?

Phase changes and evaporative cooling also move heat; induction is an electromagnetic effect.

Heat from the Sun crosses empty space as what kind of wave?

It needs no medium, which is how the Sun's heat crosses space.

What is the absolute zero on the Fahrenheit scale?

No cooling process can reach it in a finite number of steps.

In which present-day Polish city did Fahrenheit reportedly record his 0 °F winter low of 1708–09?

The city was then known as Danzig.