The candela is the SI unit of which physical quantity?
- A.Luminous intensity
- B.Electric current
- C.Amount of substance
- D.Pressure
Correct answer
Explanation
The correct answer is A, luminous intensity, that is the brightness of a source of light in a given direction. 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.
Option B, electric current, is measured in ampere, named after the French scientist Andre-Marie Ampere. Option C, amount of substance, is measured in mole, which is the chemist's counting unit for atoms and molecules. Option D, pressure, is measured in pascal, a derived unit equal to one newton per square metre. Two related units are worth knowing alongside the candela: the lumen for luminous flux and the lux for illuminance, that is the light falling on a surface.
Read the full article: Units and Measurements: SI Units, Dimensions and Instruments
Practice Questions
View allWhat is the SI unit of force?
- 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 →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.
Read the full explanation →The SI unit of pressure is
- A.Newton
- B.Pascal
- C.Hertz
- D.Tesla
Show answer
Pressure is force divided by area, so its unit is one newton per square metre, which is given the name pascal after Blaise Pascal.
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