If Planck's constant \((h)\) and speed of light in a vacuum \((c)\) are taken as two fundamental quantities, which one of the following can, in addition, be taken to express length, mass, and time in terms of the three chosen fundamental quantities?
(a) | mass of the electron \((m_e)\) |
(b) | universal gravitational constant \((G)\) |
(c) | charge of an electron \((e)\) |
(d) | mass of proton \((m_p)\) |
Step 1: Find the dimensions of mass.
We know that the dimensions of \({h}=[{h}]=\left[{ML}^2{T}^{-1}\right]\)
\({[{C}]=\left[{LT}^{-1}\right]\left[{m}_\theta\right]={M}}\)
\({[{G}]=\left[{M}^{-1}{L}^3{T}^{-2}\right]} \)
\({[{e}]=[{AT}]\left[{m}_{{p}}\right]=[{M}]} \)
\(\frac{{hc}}{{G}}=\frac{\left[{ML}^2 {T}^{-1}\right]\left[{LT}^{-1}\right]}{\left[{M}^{-1}{L}^3 {T}^{-2}\right]}=\left[{M}^2\right] \)
\(\Rightarrow {M}=\sqrt{\frac{{hc}}{{G}}}
\)
Step 2: Find the dimensions of length.
Similarly, \( \frac{{h}}{{c}}=\frac{\left[{ML}^2 {T}^{-1}\right]}{\left[{LT}^{-1}\right]}=[{ML}]\)
\({L}=\frac{{h}}{{cM}}=\frac{{h}}{{c}} \sqrt{\frac{{G}}{{hc}}}=\frac{\sqrt{{G}}}{{c}^{3 / 2}}\)
As, \( {c}={LT}^{-1}\)
\(\Rightarrow [{T}]=\frac{[{L}]}{[{C}]}=\frac{\sqrt{{Gh}}}{{c}^{3 / 2} {C}}=\frac{\sqrt{{Gh}}}{{C}^{5 / 2}}
\)
Therefore, (a), (b), or (d) can be used to express \(L, M,\) and \(T\) in terms of three chosen fundamental quantities.
Hence, option (2) is the correct answer.
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