What is Temperature? (With Definition & Units)

The temperature has a significant role in almost every area of our everyday lives as well as in all scientific disciplines, from physics to geology. You hear about the temperature in daily weather reports. Let’s learn what is temperature, what the is the unit of temperature and how it is measured.

What is Temperature?

Temperature is the measure of the hotness or coldness of an object or material. It is measured with the help of a device called a thermometer. Temperature is the expression of thermal energy.

What Makes Temperature Differ?

The scientific temperature definition involves energy, and this is what makes temperature different from measuring heat. Temperature is actually a measure of the kinetic energy of particles in an object. Particles are always moving, the faster/higher the energy, the higher the temperature.

Device Used to Measure Temperature

Temperature is measured using a device called a thermometer. There are various types of thermometers in use. The most commonly used thermometer is the glass thermometer. It uses a long thin tube that is filled with some material that moves through the tube with a change in temperature. 

There are several materials whose properties change with the temperature in a repeatable and predictable manner and this forms a way for accurate temperature measurement. Two such liquids are mercury, or sometimes alcohol. The reason why these liquids are used is that mercury and alcohol will remain liquids over a wider range of temperatures than other liquids(other liquids vapourize to gaseous form even at lower temperatures). 

The mercury rises(or expands) when the temperature is warmer and falls(or contracts) when the temperature is colder. 

So, the temperature can be determined by measuring the volume of the fluid and temperature can be read simply by observing the level of the fluid in the thermometer. Generally, we use a mercury-in-glass thermometer.

Similarly, there are a few other instruments that are used for the measurement of temperature: 

• Thermocouples
• Thermistors
• Infrared thermometer
• Resistance temperature detector (RTD)
• Pyrometer
• Langmuir probes (for measuring electron temperature of a plasma)

Units Of Temperature Measure

The unit used to represent temperature is degree $\left(^{\circ} \right)$ and it is measured using three different degrees. Temperature is measured with thermometers that may be calibrated to a variety of temperature scales because it is a relative measurement. For accurate measurement of temperature, scales based on reference points must be used. There are three main scales commonly used to measure temperature:

• Celsius: Its symbol is degree Celsius $\left(^{\circ}C \right)$. The most common form of measuring temperature in day-to-day situations. 
• Fahrenheit: Its symbol is degree Fahrenheit $\left(^{\circ}F \right)$. The less common form of measuring temperature, although some countries like the United States use this scale as their main temperature unit.
• Kelvin: Its symbol is Kelvin (K). Kelvin is used in cases of extreme heat or cold – most often in scientific environments. $0$ Kelvin is also known as absolute zero, theoretically, this is where particles are not moving at all, although this would never be observed naturally.

Temperature Conversion Between Three Different Scales

Using conversion formulas, temperatures can be converted from one scale to another. In temperature conversion the value of temperature changes from one unit to another. The three main conversions of temperature are:

Between Celsius and Kelvin

The relations between Celsius and Kelvin scales are given by 

• $K = C + 273.15$ to convert from Celsius to Kelvin
• $C = K – 273.15$ to convert from Kelvin to Celsius

Examples

Ex 1: Express $37^{\circ}C$ in the Kelvin scale

$K = C + 273.15 = 37 + 273.15 = 310.15 K$

Ex 2: Express $250 K$ in the Celsius scale

$C = K – 273.15 = – 273.15 + 250 = -23.15^{\circ}C$

Between Fahrenheit and Kelvin

The relations between Fahrenheit and Kelvin scales are given by

• $K = \frac {5}{9} \left(F – 32 \right) + 273.15$
• $F = \frac {9}{5} \left(K – 273.15 \right) + 32$

Examples

Ex 1: Express $54^{\circ}F$ in the Kelvin scale

$K = \frac {5}{9} \left(F – 32 \right) + 273.15 = \frac {5}{9} \left(54 – 32 \right) + 273.15 = \frac {5}{9} \times 22 + 273.15 = 12.22 + 273.15 = 285.37 K$

Ex 2: Express $285 K$ in the Fahrenheit scale

$F = \frac {9}{5} \left(K – 273.15 \right) + 32 = \frac {9}{5} \left(285 – 273.15 \right) + 32 = \frac {9}{5} \times 11.85 + 32 = 21.33 + 32 = 53.33^{\circ}F$

Between Celsius and Fahrenheit

The relations between Celsius and Fahrenheit scales are given by

• $C = \frac {5}{9} \left(F – 32 \right)$
• $F = \frac {9}{5}C + 32$

Examples

Ex 1: Express $82^{\circ}F$ in the Celsius scale

$C = \frac {5}{9} \left(F – 32 \right) = \frac {5}{9} \left(82 – 32 \right) = \frac {5}{9} \times 50 = 27.78^{\circ}F$

Ex 2: Express $35^{\circ}C$ in the Fahrenheit scale

$F = \frac {9}{5}C + 32 = \frac {9}{5}\times 35 + 32  = 9527.78^{\circ}C$

Note: The Fahrenheit and Celsius scales have one point at which they intersect. They are equal at $-40{\circ}C$ and $-40{\circ}F$.

Temperature and the Human Body

Temperature affects a number of physical processes, it’s therefore really important in keeping our bodies healthy and functioning properly.

The normal temperature of a human body is $36.5^{\circ}C –37.5^{\circ}C$. At this temperature, bodies are able to function normally.

When our temperature rises, this can be an indication that we’re unwell – this is called a fever. This is because our bodies are working harder to fight off an infection. These soldiers of our body are white blood cells(WBC).

What Happens to Our Bodies in Warmer or Colder Weather?

As temperature rises, our heart rate increases, and blood flow increases, and it’s pumped to the skin’s surface and we begin the sweat. This is our body’s way of cooling us down, and as the sweat evaporates, it takes the heat with it. If our body temperature rises too high, our muscles begin working slower and heat exhaustion can occur. Above $41^{\circ}C$, our bodies can begin to shut down as chemical processes that occur in the body are affected.

Our bodies will begin to shiver in colder weather. This is our muscles acting to warm us up by generating heat. If our body temperatures drop too low, our heart rate slows and our regular body functions can’t work normally. This condition of the body is called hypothermia.

Conclusion

Temperature is the measure of the hotness or coldness of an object or material. It is actually a measure of the kinetic energy of particles in an object and has three widely used scales, viz., Celsius, Fahrenheit, and Kelvin.

Practice Problems

1. Temperature is the measure of
   • hotness
   • coldness
   • Both hotness and coldness
   • None of these
2. What makes temperature differ
   • kinetic energy
   • potential energy
   • Both kinetic and potential energy
   • None of these
3. State True or False
   • $C = K + 273.15$
   • $C = K – 273.15$
   • $F = \frac {9}{5} \left(K – 273.15 \right) + 32$
   • $F = \frac {9}{5} \left(K – 32 \right) + 273.15$
   • $C = \frac {5}{9} \left(F – 32 \right)$
   • $C = \frac {5}{9} \left(F + 32 \right)$
   • $40^{\circ}C = 40^{\circ}F$
   • $-40^{\circ}C = -40^{\circ}F$
4. Convert the following temperatures as indicated
   • $235 K$ to Celsius
   • $59^{\circ}C$ to Fahrenheit
   • $196^{\circ}C$ to Kelvin
   • $75^{\circ}F$ to Celsius
   • $12^{\circ}F$ to Kelvin

Recommended Reading

• What is Length? (With Definition, Unit & Conversion)
• Weight – Definition, Unit & Conversion
• What is Capacity (Definition, Units & Examples)
• What is Time? (With Definition, Facts & Examples)

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