Light year is a unit of measurement of
- A.very large distances
- B.time interval in years
- C.amount of light received on earth in a year
- D.mass of atoms
Correct answer
Explanation
The correct answer is A, very large distances. A light year is the distance that light travels through a vacuum in one year, so despite the word year it measures length, not time. Light moves at about 3 lakh km per second, so one light year is roughly 9.46 × 10^12 km, nearly ten trillion kilometres. Astronomers use it for distances between stars and galaxies; the nearest star after the Sun, Proxima Centauri, is about 4.2 light years away. Two other large units are the astronomical unit, the mean Earth-Sun distance of about 15 crore km, and the parsec, about 3.26 light years. Option B is wrong because time is measured in seconds or years, not in light years. Option C is wrong because the light received on Earth is measured as energy or intensity, not with this unit. Option D is wrong because the mass of atoms is given in atomic mass units. Exam tip: light year = distance; 1 parsec ≈ 3.26 light years.
Practice Questions
View allSoap solution used for cleaning purpose appears cloudy. This is due to the fact that soap micelles can
- A.refract light
- B.scatter light
- C.diffract light
- D.polarize light
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Soap micelles are large enough to scatter the light passing through the solution, and this scattering makes soapy water look cloudy.
Read the full explanation →Lactose is made up of :
- A.Glucose only
- B.Glucose and Fructose
- C.Glucose and Sucrose
- D.Glucose and Galactose
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Lactose, the sugar of milk, is a disaccharide formed when one molecule of glucose joins one molecule of galactose. Disaccharides are sugars made of two simple sugar units, or monosaccharides, linked by a glycosidic bond.
Read the full explanation →In total internal reflection, the light travels from
- A.rarer to denser medium and it occurs with no loss of intensity
- B.denser to rarer medium and it occurs with no loss of intensity
- C.rarer to denser medium and it occurs with loss of intensity
- D.denser to rarer medium and it occurs with loss of intensity
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Total internal reflection happens only when light inside a denser medium meets the boundary with a rarer one at an angle larger than the critical angle, and all of the light is reflected back.
Read the full explanation →In graphite, each carbon atom is bonded to three other carbon atoms
- A.forming a three-dimensional structure
- B.in the same plane giving a hexagonal array
- C.in the same plane giving a square array
- D.in the same plane giving a pentagonal array
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In graphite each carbon atom is joined to three others in a flat layer of hexagonal rings, like a honeycomb.
Read the full explanation →Consider the following pairs of vaccine and category/type : 1. Covaxin : Inactivated pathogen-based vaccine 2. Covishield : mRNA vaccine 3. Sputnik V : Viral vector-based vaccine Which of the pairs given above is/are correctly matched ?
- A.1 only
- B.2 and 3 only
- C.1 and 3 only
- D.1, 2 and 3
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Covaxin is an inactivated virus vaccine and Sputnik V is a viral vector vaccine, but Covishield is a viral vector vaccine, not an mRNA vaccine.
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