Light year is a unit for measurement of
- A.age of universe
- B.very small time intervals
- C.very high temperature
- D.very large distance
Correct answer
Explanation
The correct answer is D, very large distance. A light year is the distance light travels in empty space in one year, so despite its name it measures length, not time.
Light moves at about 3 lakh kilometres per second. In one year it covers about 9.46 trillion kilometres, or 9.46 × 1015 metres, and that distance is one light year. Astronomers use it because distances between stars are too vast for kilometres to be convenient. The nearest star beyond the Sun, Proxima Centauri, is about 4.2 light years away. Two related units are the astronomical unit, the mean Earth–Sun distance of about 15 crore kilometres, and the parsec, about 3.26 light years.
A is wrong because the age of the universe is given in years, about 13.8 billion years. B is wrong because very small time intervals are measured in units such as the nanosecond or shake. C is wrong because very high temperatures are measured in kelvin, and pyrometers are used to read them.
Exam tip: light year, parsec and astronomical unit are all units of distance; parsec is the largest, the astronomical unit the smallest.
Practice Questions
View allWho among the following built a model steam engine in 1698 called "Miner's Friend" to drain mines ?
- A.Thomas Savery
- B.Thomas Newcomen
- C.James Watt
- D.Richard Arkwright
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The English engineer Thomas Savery patented a steam pump in 1698 and called it the Miner's Friend, as it was meant to pump water out of flooded mines.
Read the full explanation →A metallic wire having resistance of 20 Ω is cut into two equal parts in length. These parts are then connected in parallel. The resistance of this parallel combination is equal to
- A.20 Ω
- B.10 Ω
- C.5 Ω
- D.15 Ω
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Each half of the wire has a resistance of 10 Ω, and two 10 Ω resistors in parallel give 5 Ω. The resistance of a wire is R = ρL/A, so it is directly proportional to its length when the material and thickness stay the same.
Read the full explanation →Myopia is a defect in human vision where an image of a
- A.nearby object is focused beyond the retina.
- B.nearby object is focused before the retina.
- C.distant object is focused before the retina.
- D.distant object is focused beyond the retina.
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In myopia, or short-sightedness, a person sees near objects clearly but distant objects look blurred because their image forms in front of the retina.
Read the full explanation →A homogeneous mixture contains two liquids. How are they separated ?
- A.By filtration
- B.By evaporation
- C.By distillation
- D.By condensation
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Two miscible liquids that form a homogeneous mixture are separated by distillation, which uses the difference in their boiling points.
Read the full explanation →Cartilage is NOT found in
- A.larynx
- B.nose
- C.ear
- D.urinary bladder
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The urinary bladder is a hollow muscular sac made of smooth muscle and a stretchable lining; it has no cartilage.
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