MCQ
Consider three quantities $\text{x}=\frac{\text{E}}{\text{B}},\ \text{y}=\sqrt{\frac{1}{\mu_0\in_0}}$ and $\text{z}=\frac{1}{\text{CR}}.$ Here, l is the length of a wire, C is a capacitance and R is a resistance. All other symbols have standard meanings.
  • A
    x, y have the same dimensions.
  • B
    y, z have the same dimensions.
  • C
    z, x have the same dimensions.
  • All of the above.

Answer

Correct option: D.
All of the above.
Explanation:
Lorentz Force:
$\text{qvB}=\text{qE}$
⇒ Dimensions of $\text{x}=[\text{v}]=\Big[\frac{\text{E}}{\text{B}}\Big]=\big[\text{LT}^{-1}\big]$
$\text{y}=\frac{1}{\sqrt{\mu_0\in_0}}=\sqrt{\frac{4\pi}{\mu_0}\times\frac{1}{4\pi\in_0}}=\sqrt{\frac{9\times10^9}{10^{-7}}}=3\times10^8=\text{c}$
⇒ Dimensions of $\text{y}=[\text{c}]=\big[\text{LT}^{-1}\big]$
Time constant of RC circuit = RC so dimensionally [RC] = [T]
$\Rightarrow\text{z}=\Big[\frac{\text{l}}{\text{RC}}\Rightarrow[\text{z}]=[\text{LT}^{-1}]$
Therefore, x, y and z have the same dimensions.

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