The Beauty of Dimensional Analysis
Imagine you are an explorer in the vast universe of physics, and your most trusted compass is Dimensional Analysis. It is the ultimate truth-teller, the universal translator that strips away the complexity of any physical quantity and reveals its fundamental DNA: Mass (M), Length (L), Time (T), and Current (A).
In this epic problem, we are tasked with decoding four of the most profound quantities in electromagnetism: Capacitance, Permittivity, Permeability, and the Electric Field. Let's break them down one by one.
Decoding Capacitance (C)
Capacitance is the ability of a system to store electric charge. Mathematically, it is defined as the charge stored per unit potential difference:
But what is potential (V)? Potential is simply the work done per unit charge (V=W/q). Substituting this into our capacitance equation gives us a much friendlier form:
Now, we just plug in the fundamental dimensions. Charge q is current times time, so [q]=[AT]. Work W is force times distance, so [W]=[ML2T−2].
[C]=[ML2T−2][AT]2=[M−1L−2T4A2]
This perfectly matches option III in our list.
Unveiling Permittivity (ε0)
Permittivity of free space tells us how much resistance a vacuum offers to the formation of an electric field. The easiest way to find its dimensions is to summon Coulomb's Law:
By isolating ε0, we get:
We know the dimensions of force ([MLT−2]), charge ([AT]), and distance ([L]). Let's substitute them in:
[ε0]=[MLT−2][L2][AT]2=[M−1L−3T4A2]
This matches option II.
The Speed of Light Trick for Permeability (μ0)
Permeability of free space is the magnetic counterpart to permittivity. While you could use the Biot-Savart law or Ampere's law to find its dimensions, there is a much more elegant trick. James Clerk Maxwell showed us that the speed of light in a vacuum is intimately connected to these two constants:
Squaring both sides and rearranging for μ0 gives:
We already did the hard work of finding [ε0]. The speed of light c is just a velocity, so [c]=[LT−1]. Let's plug these in:
[μ0]=[M−1L−3T4A2][LT−1]21
Simplifying the denominator and bringing the terms to the numerator yields:
This matches option IV.
The Simplicity of the Electric Field (E)
Finally, we arrive at the Electric Field. An electric field is simply the electrostatic force experienced per unit charge:
This is the most straightforward calculation of the bunch. We divide the dimensions of force by the dimensions of charge:
[E]=[AT][MLT−2]=[M1L1T−3A−1]
This matches option I.
Bringing It All Together
By systematically breaking down each complex quantity into fundamental mechanical dimensions, we have successfully decoded the entire matrix:
- A. Capacitance → III
- B. Permittivity → II
- C. Permeability → IV
- D. Electric Field → I
This perfectly aligns with the first option provided in the question. Dimensional analysis is not just a tool for solving problems; it is a profound way to see the underlying unity of the physical world.