Dimensionless Quantities

Question

Which is dimensionless?

RankGuru · Accepted Answer

Dimensionless quantities are ratios of similar physical quantities.
1. **Strain**: $\Delta L / L$ (Length / Length). Dimensionless.
2. **Refractive Index**: $c_{vacuum} / c_{medium}$ (Speed / Speed). Dimensionless.
3. **Angle**: $	ext{Arc length} / 	ext{Radius}$ (Length / Length). Dimensionless.
Even though angles have units (degrees/radians), they do not have physical dimensions ($M, L, T$).

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Dimensionless Quantities

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