# Temperature - Definition, Measurement, Temperature Units

## Introduction:

Quite often, we confuse temperature with heat and regard them to be the same. It is important to realise that heat is a form of energy while the temperature is something different. Temperature refers to the hotness or coldness of a body. In specific terms, it is the way of determining the kinetic energy of particles within an object, a kind of energy that is associated with the motion. Faster the movement of particles; more the temperature and vice versa.

To determine how hot an iron rod is, physicists measure it in temperature to be precise rather than mentioning how hot or cold the rod is.

Temperature is important in all fields of Science right from Physics to Geology and also it is crucial in most aspects of our daily life.

## Relationship Between Temperature and Kinetic Energy

Kinetic energy is the energy possessed by a body due to its motion. We see a range of kinetic energy in molecules because molecules don’t move at the same speed. When a substance absorbs heat, the particles move faster so the average kinetic energy and therefore the temperature increases.

The Kelvin temperature scale possesses a true zero with no negative temperatures. Zero Kelvin is called absolute zero. It’s the lowest temperature theoretically achievable and is the temperature at which the particles in a perfect crystal would become motionless.

Solids, liquids and gases all have a temperature. The particles within a solid don’t move, but they have vibrational motion. The temperature increases when molecules vibrate faster. The melting point of a solid is the temperature at which the vibrational motion overcomes the forces of attraction holding the molecules in a solid formation.

## Temperature Measurement

Temperature is the measure of the heat in the body. Temperature identifies the body as hot or cold. The SI unit used to measure the temperature in Kelvin(K). The other scales used to measure the temperature are Celsius or Fahrenheit. The instrument which is used for measuring temperature is a thermometer.

### What is a Temperature Sensor?

A temperature sensor is an RTD (resistance temperature detector) or a thermocouple, that collects the data about temperature from a particular source and converts the data into an understandable form for a device or an observer. Temperature sensors are used in many applications such as food processing units and medical devices.

The most common type of temperature sensor is the thermometer, which measures the temperature of solids, liquids and gases. It is also a common type of temperature sensor mostly used for non-scientific purposes because it is not so accurate. Following are a few temperature sensors besides thermometer.

• Thermocouples
• Resistor temperature detectors
• Thermistors
• Infrared sensors
• Semiconductors

### How Does a Thermometer Measure Temperature?

Thermometers are the most common instrument to measure temperature. The simplest of thermometers is the liquid thermometer. They are a thin glass tube filled with a small amount of mercury.  Thermometers measure the temperature due to thermal expansion. Increase in the volume of substance because of the increase in the temperature is known as Thermal expansion. A small change in the temperature causes changes in the volume of a liquid.  However, this form of effect is maximized when the liquid expands within the thin tube of the thermometer. When mercury gets hotter, it increases in size by an amount that’s directly related to the temperature. So if the temperature increases by 20 degrees, the mercury expands and moves up the scale by twice as much as if the temperature increase is only 10 degrees.

Making a Celsius scale is easier because it’s based on the temperatures of ice and boiling water. These are the two fixed points. When we dip the thermometer into ice, we observe that the mercury level marks the lowest point on our scale i.e, 0°C.  Similarly, if we dip the thermometer in boiling water, mercury rises up and marks 100°C.  The scale of a thermometer is divided between 0°C and 100°C into 100 equal parts.

### Temperature Units:

Some units of temperature, degrees Fahrenheit and degrees Celsius. Kelvin is another unit of temperature that is very handy for many scientific calculations, since it begins at absolute zero, meaning it has no negative numbers. The relation between Fahrenheit, Celsius & Kelvin –

#### Fahrenheit to Celsius:

$\large ^{\circ }C= \frac{\left ( ^{\circ }F-32 \right )}{1.8}$

#### Celsius to Kelvin:

$\large K =\: ^{\circ }C + 273$

### Effects of Temperature:

An increase or decrease in temperature causes various changes in the physical and chemical processes of life. Some of those are given below-

• It affects the solubility, density, vapour pressure, physical properties of various materials along with the electrical conductivity
• The rate of a chemical reaction is also affected by the temperature.
• The thermal radiations from the surface of objects are also affected by temperature.