In Milikan's Method, the radius of droplet can be calculated by:
Correct answer: C. r2 = 9ηvt / 2ρg
- A. r = √qvt / 2ρg
- B. r2 = 9ηvt / ρg
- C. r2 = 9ηvt / 2ρg
- D. r = 9ηvt / 2ρg
Explanation
Explanation If ρ is the density of the droplets then its volune can be expressed as: V = 4/3 πr³As, ρ = m / VSo, ρ = m / (4/3 πr³ρ) m = 4/3 πr³ρ ----------(1)Using strokes law: 6πηrvt = mg m = 6πηrvt / g -------------(2)Comparing equation (1) and (2), we get 6πηrvt /g = 4/3 πr³ρ r² = 9ηvt / 2ρg
This question appeared on the UHS MDCAT 2009 paper, which you can sit online with every answer explained.
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Fluid drag is the resistive force exerted by a liquid or gas on an object moving through it, and its value depends on speed, fluid density, shape and exposed area. Questions examine drag at low and high speeds, terminal velocity when drag balances weight, and the difference between drag and ordinary solid friction.
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