Why do most of the physical equations have $\frac{1}{4\pi}$ as constants? I have seen that many equations have $\frac{1}{4\pi}$ as constants like Coulomb, pendulum problems, etc. Can anyone tell me why is like this?
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It is--for thing involving Gauss's law, because there are $4\pi$ steradians in total. That is, integrating over every direction gives:
$$ {\rlap{\large{\circ}}} {\rlap{{\hspace{15px} \large{\circ}}}} {\rlap{\raise{-7px}{\hspace{5px} {\color{white}{\rule{15px}{20px}}}}}} {\rlap{\raise{-0px}{\hspace{5px} \rule{15px}{1px} }}} {\rlap{\raise{9px}{\hspace{5px} \rule{15px}{1px} }}} {\rlap{\iint}} {\phantom{\iint}} \, \mathrm{d}\Omega=\int_{\theta=0}^{\pi}{\int_{\phi=0}^{2\pi}{\sin{\theta} \, \mathrm{d}\theta \, \mathrm{d}\phi}}=4\pi $$
