A length - scale l depends on the permittivity ε of a dielectric material, Boltzmann constant k B , the absolute temperature T, the number per unit volume (n) of certain charged particles, and the cha

Question

A length - scale l depends on the permittivity ε of a dielectric material, Boltzmann constant k B , the absolute temperature T, the number per unit volume (n) of certain charged particles, and the charge (q) carried by each of the particles, Which of the following expressions (s) for l is (are) dimensionally correct?

TestHub · Accepted Answer

We know, F = 1 4 π E 0 q 2 r 2 ⇒ q 2 E 0 = F r 2 4 π So, dimension q 2 E 0 = dim ⁡ F r 2 = M L T - 2 × L 2 = M L 3 T - 2 Similarly; E = 3 2 K B T ⇒ dim ⁡ K B T = dim ⁡ E n e r g y = M L 2 T - 2 (i) n q 2 E k B T = L - 3 × M L 3 T - 2 M L 2 T - 2 = 1 L (ii) E × v o l F r 2 = M L T - 2 × L 3 M L T - 2 × L 2 = L (iii) F r 2 v o l 2 3 ( K ℇ ) = M L T - 2 × L 2 × L 2 M L 2 T - 2 = L 3 = L 3 2 (iv) F r 2 v o l 1 3 E n e r g y = M L T - 2 L 2 × L M L 2 T - 2 = L [ ∴ dimension n = dim 1 v o l = L - 3 ]

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