\(\frac{1}{4} = {e^{ - \mu (3.5\,mm)}} \Rightarrow \,{e^{\mu (3.5\,mm)}} = 4\)
\(\mu = \frac{{{{\log }_e}4}}{{3.5mm}} = \frac{{2\ell n2}}{{3.5\,mm}} = \frac{{2 \times 0.693}}{{3.5mm}} \approx \,\,\frac{{2 \times 0.7}}{{3.5\,mm}}\)
\(=0.4\,\,m{m^{ - 1}}\)
$\left(\frac{1}{4 \pi \epsilon_0}=9 \times 10^9 \mathrm{SI}\right.$ એકમ $\alpha$ કણનું દળ $=$ $\left.6.72 \times 10^{-27} \mathrm{~kg}\right)$