Source: Extra Practice

What are the dimensions of the product LCLC, where LL is inductance and CC is capacitance?

Options

Option A

[T][T]

Option B

[T1][T^{-1}]

Option C is correct

[T2][T^2]

Option D

[M0L0T0][M^0L^0T^0]

Explanation

In an LC circuit, the resonant angular frequency ω\omega is given by ω=1LC\omega = \frac{1}{\sqrt{LC}}. The dimension of angular frequency ω\omega is [T1][T^{-1}] (since ω=2π/T\omega = 2\pi/T, where TT is period). From the formula, we have 1[LC]=[T1]\frac{1}{\sqrt{[LC]}} = [T^{-1}]. This implies [LC]=[T]\sqrt{[LC]} = [T]. Squaring both sides gives [LC]=[T2][LC] = [T^2]. Alternatively, one can find the dimensions of L and C separately: Inductance LL: From Faraday's law, V=LdIdtV = L \frac{dI}{dt}, so [L]=[V][I][T1][L] = \frac{[V]}{[I][T^{-1}]}. Since V=W/Q=W/(IT)V = W/Q = W/(IT), [V]=[ML2T2][AT]=[ML2T3A1][V] = \frac{[ML^2T^{-2}]}{[AT]} = [ML^2T^{-3}A^{-1}]. Therefore, [L]=[ML2T3A1][A][T1]=[ML2T2A2][L] = \frac{[ML^2T^{-3}A^{-1}]}{[A][T^{-1}]} = [ML^2T^{-2}A^{-2}]. Capacitance CC: From Q=CVQ = CV, so C=Q/VC = Q/V. Since Q=ITQ = IT, [C]=[AT][ML2T3A1]=[M1L2T4A2][C] = \frac{[AT]}{[ML^2T^{-3}A^{-1}]} = [M^{-1}L^{-2}T^4A^2]. Multiplying [L][L] and [C][C]: [LC]=[ML2T2A2]×[M1L2T4A2]=[M11L22T2+4A2+2]=[M0L0T2A0]=[T2][LC] = [ML^2T^{-2}A^{-2}] \times [M^{-1}L^{-2}T^4A^2] = [M^{1-1}L^{2-2}T^{-2+4}A^{-2+2}] = [M^0L^0T^2A^0] = [T^2].