'Optical density' of a medium is:
AThe same as mass density (ρ = m/V)
BA measure of how light slows in the medium (= refractive index); NOT the same as mass density. E.g., turpentine has lower mass density than water but higher optical density
CSimply the colour of the medium
DThe mass per unit refractive index
Answer & Solution
Correct answer: B. A measure of how light slows in the medium (= refractive index); NOT the same as mass density. E.g., turpentine has lower mass density than water but higher optical density
**Optical density ≠ mass density**. Optical density relates to the **speed of light** in the medium (effectively the refractive index). The two can be uncorrelated: turpentine (mass density ~0.85 g/mL) has *higher* optical density than water (density 1.00 g/mL).
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