Learning Scientific Programming with Python (2nd edition)
P2.3.2: String formatting and physical constants
Question P2.3.2
The table below gives the names, symbols, values, uncertainties and units of some physical constants.
| Name | Symbol | Value | Uncertainty | Units |
|---|---|---|---|---|
| Boltzmann constant | $k_\mathrm{B}$ | $1.3806504\times10^{-23}$ | $2.4\times 10^{-29}$ | $\mathrm{J\,K^{-1}}$ |
| Speed of light | $c$ | $299792458$ | (def) | $\mathrm{m\,s^{-1}}$ |
| Planck constant | $h$ | $6.62606896 \times 10^{-34}$ | $3.3\times 10^{-41}$ | $\mathrm{J\,s}$ |
| Avogadro constant | $N_\mathrm{A}$ | $\;\;\,6.02214179 \times 10^{23}$ | $3\times 10^{16}$ | $\mathrm{mol^{-1}}$ |
| Electron magnetic moment | $\mu_e$ | $-9.28476377 \times 10^{-24}$ | $2.3\times 10^{-31}$ | $\mathrm{J/T}$ |
| Gravitational constant | $G$ | $\;\;\,6.67428 \times 10^{-11}$ | $6.7 \times 10^{-15}$ | $\mathrm{N\,m^2\,kg^{-2}}$ |
Defining variables of the form:
kB = 1.3806504e-23 # J/K
kB_unc = 2.4e-29 # uncertainty
kB_units = 'J/K'
use the string object's format method to produce the following output:
(a)
kB = 1.381e-23 J/K
(b)
G = 0.0000000000667428 Nm^2/kg^2
(c) Using the same format specifier for each line,
kB = 1.3807e-23 J/K
mu_e = -9.2848e-24 J/T
N_A = 6.0221e+23 mol-1
c = 2.9979e+08 m/s
(d) Again, using the same format specifier for each line,
=== G = +6.67E-11 [N m2 kg-2] ===
=== μe = -9.28E-24 [ J/T] ===
Hint: The Unicode codepoint for, μ, the lower case greek letter mu, is U+03BC.
(e) (Harder). Produce the output below, in which the uncertainty (one standard deviation) in the value of each constant is expressed as a number in parentheses relative the the preceding digits: that is, $6.62606896(33) \times 10^{-34}$ means $6.62606896 \times 10^{-34} \pm 3.3 \times 10^{-41}$.
G = 6.67428(67)e-11 Nm2/kg2
mu_e = -9.28476377(23)e-24 J/T