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<a name="Introduction-to-physical_005fconstants"></a>
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Next: <a href="maxima_265.html#Functions-and-Variables-for-ezunits" accesskey="n" rel="next">Functions and Variables for ezunits</a>, Previous: <a href="maxima_263.html#Introduction-to-ezunits" accesskey="p" rel="previous">Introduction to ezunits</a>, Up: <a href="maxima_262.html#ezunits_002dpkg" accesskey="u" rel="up">ezunits-pkg</a> [<a href="maxima_toc.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="maxima_423.html#Function-and-Variable-Index" title="Index" rel="index">Index</a>]</p>
</div>
<a name="Introduction-to-physical_005fconstants-1"></a>
<h3 class="section">57.2 Introduction to physical_constants</h3>
<a name="physical_005fconstants"></a><p><code>physical_constants</code> is a collection of physical constants,
copied from CODATA 2006 recommended values
(<a href="https://physics.nist.gov/cuu/Constants/">https://physics.nist.gov/cuu/Constants/</a>).
<code>load ("physical_constants")</code> loads this package,
and loads <code>ezunits</code> also, if it is not already loaded.
</p>
<p>A physical constant is represented as a symbol which has a property
which is the constant value.
The constant value is a dimensional quantity, as represented by <code>ezunits</code>.
The function <code>constvalue</code> fetches the constant value;
the constant value is not the ordinary value of the symbol,
so symbols of physical constants persist in evaluated expressions until their
values are fetched by <code>constvalue</code>.
</p>
<p><code>physical_constants</code> includes some auxiliary information,
namely, a description string for each constant,
an estimate of the error of its numerical value,
and a property for TeX display.
To identify physical constants, each symbol has the
<code>physical_constant</code> property;
<code>propvars(physical_constant)</code> therefore shows the list
of all such symbols.
</p>
<p><code>physical_constants</code> comprises the following constants.
</p>
<dl compact="compact">
<dt><code>%c</code></dt>
<dd><p>speed of light in vacuum
</p></dd>
<dt><code>%mu_0</code></dt>
<dd><p>magnetic constant
</p></dd>
<dt><code>%e_0</code></dt>
<dd><p>electric constant
</p></dd>
<dt><code>%Z_0</code></dt>
<dd><p>characteristic impedance of vacuum
</p></dd>
<dt><code>%G</code></dt>
<dd><p>Newtonian constant of gravitation
</p></dd>
<dt><code>%h</code></dt>
<dd><p>Planck constant
</p></dd>
<dt><code>%h_bar</code></dt>
<dd><p>Planck constant
</p></dd>
<dt><code>%m_P</code></dt>
<dd><p>Planck mass
</p></dd>
<dt><code>%T_P</code></dt>
<dd><p>Planck temperature
</p></dd>
<dt><code>%l_P</code></dt>
<dd><p>Planck length
</p></dd>
<dt><code>%t_P</code></dt>
<dd><p>Planck time
</p></dd>
<dt><code>%%e</code></dt>
<dd><p>elementary charge
</p></dd>
<dt><code>%Phi_0</code></dt>
<dd><p>magnetic flux quantum
</p></dd>
<dt><code>%G_0</code></dt>
<dd><p>conductance quantum
</p></dd>
<dt><code>%K_J</code></dt>
<dd><p>Josephson constant
</p></dd>
<dt><code>%R_K</code></dt>
<dd><p>von Klitzing constant
</p></dd>
<dt><code>%mu_B</code></dt>
<dd><p>Bohr magneton
</p></dd>
<dt><code>%mu_N</code></dt>
<dd><p>nuclear magneton
</p></dd>
<dt><code>%alpha</code></dt>
<dd><p>fine-structure constant
</p></dd>
<dt><code>%R_inf</code></dt>
<dd><p>Rydberg constant
</p></dd>
<dt><code>%a_0</code></dt>
<dd><p>Bohr radius
</p></dd>
<dt><code>%E_h</code></dt>
<dd><p>Hartree energy
</p></dd>
<dt><code>%ratio_h_me</code></dt>
<dd><p>quantum of circulation
</p></dd>
<dt><code>%m_e</code></dt>
<dd><p>electron mass
</p></dd>
<dt><code>%N_A</code></dt>
<dd><p>Avogadro constant
</p></dd>
<dt><code>%m_u</code></dt>
<dd><p>atomic mass constant
</p></dd>
<dt><code>%F</code></dt>
<dd><p>Faraday constant
</p></dd>
<dt><code>%R</code></dt>
<dd><p>molar gas constant
</p></dd>
<dt><code>%%k</code></dt>
<dd><p>Boltzmann constant
</p></dd>
<dt><code>%V_m</code></dt>
<dd><p>molar volume of ideal gas
</p></dd>
<dt><code>%n_0</code></dt>
<dd><p>Loschmidt constant
</p></dd>
<dt><code>%ratio_S0_R</code></dt>
<dd><p>Sackur-Tetrode constant (absolute entropy constant)
</p></dd>
<dt><code>%sigma</code></dt>
<dd><p>Stefan-Boltzmann constant
</p></dd>
<dt><code>%c_1</code></dt>
<dd><p>first radiation constant
</p></dd>
<dt><code>%c_1L</code></dt>
<dd><p>first radiation constant for spectral radiance
</p></dd>
<dt><code>%c_2</code></dt>
<dd><p>second radiation constant
</p></dd>
<dt><code>%b</code></dt>
<dd><p>Wien displacement law constant
</p></dd>
<dt><code>%b_prime</code></dt>
<dd><p>Wien displacement law constant
</p></dd>
</dl>
<p>Reference: <a href="https://physics.nist.gov/cuu/Constants/">https://physics.nist.gov/cuu/Constants/</a>
</p>
<p>Examples:
</p>
<p>The list of all symbols which have the <code>physical_constant</code> property.
</p>
<div class="example">
<pre class="example">(%i1) load ("physical_constants")$
(%i2) propvars (physical_constant);
(%o2) [%c, %mu_0, %e_0, %Z_0, %G, %h, %h_bar, %m_P, %T_P, %l_P,
%t_P, %%e, %Phi_0, %G_0, %K_J, %R_K, %mu_B, %mu_N, %alpha,
%R_inf, %a_0, %E_h, %ratio_h_me, %m_e, %N_A, %m_u, %F, %R, %%k,
%V_m, %n_0, %ratio_S0_R, %sigma, %c_1, %c_1L, %c_2, %b, %b_prime]
</pre></div>
<p>Properties of the physical constant <code>%c</code>.
</p>
<div class="example">
<pre class="example">(%i1) load ("physical_constants")$
(%i2) constantp (%c);
(%o2) true
(%i3) get (%c, description);
(%o3) speed of light in vacuum
(%i4) constvalue (%c);
m
(%o4) 299792458 ` -
s
(%i5) get (%c, RSU);
(%o5) 0
(%i6) tex (%c);
$$c$$
(%o6) false
</pre></div>
<p>The energy equivalent of 1 pound-mass.
The symbol <code>%c</code> persists until its value is fetched by <code>constvalue</code>.
</p>
<div class="example">
<pre class="example">(%i1) load ("physical_constants")$
(%i2) m * %c^2;
2
(%o2) %c m
(%i3) %, m = 1 ` lbm;
2
(%o3) %c ` lbm
(%i4) constvalue (%);
2
lbm m
(%o4) 89875517873681764 ` ------
2
s
(%i5) E : % `` J;
Computing conversions to base units; may take a moment.
366838848464007200
(%o5) ------------------ ` J
9
(%i6) E `` GJ;
458548560580009
(%o6) --------------- ` GJ
11250000
(%i7) float (%);
(%o7) 4.0759872051556356e+7 ` GJ
</pre></div>
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Categories:<a href="maxima_424.html#Category_003a-Physical-units">Physical units</a>
·<a href="maxima_424.html#Category_003a-Share-packages">Share packages</a>
·<a href="maxima_424.html#Category_003a-Package-physical_005fconstants">Package physical_constants</a>
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<a name="Item_003a-ezunits_002fnode_002fFunctions-and-Variables-for-ezunits"></a><hr>
<div class="header">
<p>
Next: <a href="maxima_265.html#Functions-and-Variables-for-ezunits" accesskey="n" rel="next">Functions and Variables for ezunits</a>, Previous: <a href="maxima_263.html#Introduction-to-ezunits" accesskey="p" rel="previous">Introduction to ezunits</a>, Up: <a href="maxima_262.html#ezunits_002dpkg" accesskey="u" rel="up">ezunits-pkg</a> [<a href="maxima_toc.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="maxima_423.html#Function-and-Variable-Index" title="Index" rel="index">Index</a>]</p>
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