Which instrument is used to test the purity of milk?
- A.Hydrometer
- B.Lactometer
- C.Pyrometer
- D.Fathometer
Correct answer
Explanation
The correct answer is B, lactometer. A lactometer floats in milk and shows its relative density. Pure milk is denser than water, so adding water lowers the density and the instrument sinks deeper, which reveals the adulteration. It is in effect a hydrometer calibrated for one particular liquid.
Option A, the hydrometer, measures the relative density of liquids in general, so it is the parent instrument rather than the specific answer this question wants. Option C, the pyrometer, measures very high temperatures, such as those inside a furnace, without touching the hot body. Option D, the fathometer, measures the depth of the sea using sound waves. Instrument questions are pure pairing questions, so revise them as a table rather than one at a time. A lactometer is therefore read where its stem meets the surface of the milk, and a reading below the pure-milk mark points to added water.
Read the full article: Units and Measurements: SI Units, Dimensions and Instruments
Practice Questions
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- A.Joule
- B.Newton
- C.Watt
- D.Pascal
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One newton is the force that gives a mass of one kilogram an acceleration of one metre per second squared, which follows directly from the equation force equals mass times acceleration.
Read the full explanation →How many base units are there in the International System of Units (SI)?
- A.Five
- B.Six
- C.Seven
- D.Nine
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The SI system, adopted in 1960 by the General Conference on Weights and Measures, rests on seven base units: the metre, the kilogram, the second, the ampere, the kelvin, the mole and the candela.
Read the full explanation →Which one of the following is NOT a base unit of the SI system?
- A.Kelvin
- B.Mole
- C.Newton
- D.Candela
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The newton is a derived unit: it is built from the kilogram, the metre and the second, since force equals mass times acceleration, and it can be written as one kilogram metre per second squared.
Read the full explanation →The candela is the SI unit of which physical quantity?
- A.Luminous intensity
- B.Electric current
- C.Amount of substance
- D.Pressure
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The candela takes its name from the candle, which was once used as a rough standard of light, and it is one of the seven base units of the SI system.
Read the full explanation →A light year is a unit of which of the following?
- A.Time
- B.Distance
- C.Speed
- D.Brightness of a star
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A light year is the distance that light, moving at about three lakh kilometres per second, covers in one year, which works out to roughly 9.46 trillion kilometres.
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