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ElectrostaticsClass 12, Electrostatic Potential and Capacitance

Dimensional formula of Relative permittivity

[M0 L0 T0]

Symbolεr SI unitnone, a pure number

The factor by which a dielectric raises the capacitance, so it is a pure number. It is also called the dielectric constant.

Derivation

How to get the dimensional formula of relative permittivity

  1. Start from the definition: relative permittivity = capacitance / capacitance.
  2. electric charge = electric current × time, so electric charge is [A] × [T] = [T A].
  3. velocity = length / time, so velocity is [L] / [T] = [L T-1].
  4. energy = mass × velocity2, so energy is [M] × [L T-1]2 = [M L2 T-2].
  5. electric potential = energy / electric charge, so electric potential is [M L2 T-2] / [T A] = [M L2 T-3 A-1].
  6. capacitance = electric charge / electric potential, so capacitance is [T A] / [M L2 T-3 A-1] = [M-1 L-2 T4 A2].
  7. Put in the dimension of each part: [M-1 L-2 T4 A2] / [M-1 L-2 T4 A2].
  8. Add the powers of each base quantity: [M0 L0 T0].
Same dimensions

Quantities with the dimensions [M⁰ L⁰ T⁰]

Equal dimensions do not make them the same quantity. Compare relative permittivity with the others in the full grid.

Practice

Three questions on relative permittivity

1Which of these has the same dimensions as relative permittivity?

2Which of these has no dimensions at all?

3Which one has different dimensions from the others?

Questions

Relative permittivity: quick answers

What is the dimensional formula of relative permittivity?

The dimensional formula of relative permittivity is [M⁰ L⁰ T⁰]. It comes from relative permittivity = capacitance / capacitance.

What is the SI unit of relative permittivity?

Relative permittivity has no unit, because it is a pure number.

Is relative permittivity dimensionless?

Yes. Relative permittivity is a ratio of like quantities, so every power in its dimensional formula is zero: [M⁰ L⁰ T⁰].

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