# Help:Physical Constants

Level: Introductory, Intermediate

## Contents |

## Physical Constants

The values of the constants provided here are recommended for international use by CODATA and are the latest available. Termed the " 2018 CODATA recommended values," they are generally recognized worldwide for use in all fields of science and technology. The values became available on 20 May 2019 and replaced the 2014 CODATA set. They are based on all of the data available through 31 December 2018. The 2018 adjustment was carried out under the auspices of the CODATA Task Group on Fundamental Constants.

2018 CODATA recommended values (ascii)

Frequently used constants (pdf)

**References**

2018 CODATA recommended values

The CODATA 2017 Values of *h*, *e*, *k*, and N_{A} for the Revision of the SI

Also available is an Introduction to the constants for nonexperts.

#### New Definition of the Mole

After an extensive consultation with the chemistry community, and following a review and critical evaluation of the literature, IUPAC is recommending a new definition of the mole based on a specified number of elementary entities:

*The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.022 140 76 × 10 ^{23} elementary entities. This number is the fixed numerical value of the Avogadro constant, N_{A}, when expressed in mol^{−1}, and is called the Avogadro number.*

For more information, see the following links...

2019 redefinition of the SI base units

A new definition for the mole based on the Avogadro constant: a journey from physics to chemistry

A NEW DEFINITION OF THE MOLE HAS ARRIVED (IUPAC)

#### Wiki Help

More information on this application and the data sources used therein can be found by clicking on the *Help* button in the taskbar. This leads to the Wiki Help for this application.

## Conversion Factors

Conversion Factors are given for mass, energy, energy dose, ion dose, time and activity.

## Prefixes/Greek Alphabet

There is an additional tab for prefixes and the Greek alphabet.

## Radiological Limits

Radiological Limits give radiation limits for workers, apprentices and students, and members of the public. The values given are recommended by international organisations such as Euratom, ICRP, and IAEA and the national German authorities. Dose limits given are for whole and partial body (eyes, hands, skin, etc.) exposure. For apprentices and students, data is given for ages less than 16 years, 16 -18 years and over 18 years old.

See the Glossary entry on Radiological limits also for References