The power of a lens is measured in:
Answer: A
The power of a lens is measured in dioptres - the reciprocal of the focal length in metres:
\[ P = \frac{1}{f} \]
A converging lens of focal length 50 cm has a power of +2 D. Powers add when lenses are combined, which is why the unit is used in prescribing spectacles.
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What does airbag, used for safety of car driver, contain?
Answer: B
A car airbag contains sodium azide, NaN3.
A crash sensor ignites it and it decomposes in milliseconds, releasing nitrogen gas that inflates the bag:
\[ \mathrm{2NaN_3 \rightarrow 2Na + 3N_2} \]
The whole process takes about 30 milliseconds.
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Study of teeth is called
Answer: D
The study of teeth is odontology, from the Greek odous, tooth.
Forensic odontology identifies human remains from dental records. Pedagogy is the study of teaching, ornithology of birds and orthoepy of correct pronunciation.
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Which of the following parts of the sun is easily visible only during a total solar eclipse?
Answer: D
The corona is visible only during a total solar eclipse.
It is about a millionth as bright as the photosphere, so it is normally lost in the glare. When the moon covers the disc exactly, the corona appears as a pearly halo of streamers around the black moon.
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The theory which advocates that living beings can arise only from other living beings is termed
Answer: A
The theory that living things arise only from other living things is biogenesis.
It replaced the older belief in abiogenesis, or spontaneous generation, which Redi, Spallanzani and finally Pasteur disproved - Pasteur's swan-necked flask experiment of 1859 settled the question.
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What happens when some charge is placed on a soap bubble?
Answer: B
Charging a soap bubble makes its radius increase.
The like charges spread over the surface repel one another, and this outward electrostatic pressure adds to the air pressure inside, opposing the inward pull of surface tension. The bubble expands until the forces balance again.
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Seawater (i.e. saltwater) freezes at:
Answer: B
Sea water freezes at a slightly lower temperature than fresh water - about −1.9°C for water of normal salinity, against 0°C.
The dissolved salt lowers the freezing point, a colligative property that depends on the number of dissolved particles. As sea ice forms it excludes most of the salt, so the ice itself is nearly fresh.
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At present, scientists can determine the arrangement or relative positions of genes of DNA sequences on a chromosome. How does this knowledge benefit us?
1. It is possible to know the pedigree of livestock.
2. It is possible to understand the causes of all human diseases.
3. It is possible to develop disease-resistant animal breeds.
Which of the statements given above is/are correct?
Answer: D
All three statements are correct.
Gene mapping lets breeders trace ancestry from DNA alone, so livestock pedigrees can be verified; it identifies the genes behind resistance to disease, so resistant breeds can be developed; and it has revealed the genetic basis of a great many human diseases - which is the ground on which the second statement is accepted here.
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Of the following, which element is common to all acids
Answer: A
Hydrogen is the element common to all acids. An acid is defined as a substance that releases hydrogen ions (H+) in water.
Hydrochloric acid gives HCl → H+ + Cl−, sulphuric acid gives two hydrogen ions, and it is the concentration of those ions that the pH scale measures.
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Which of the following plants is not capable of manufacturing own food?
Answer: B
The mushroom cannot make its own food. It is a fungus and has no chlorophyll, so it lives as a saprophyte, absorbing nutrients from dead organic matter.
Algae, carrot and cabbage all photosynthesise; the carrot's root is a store filled by leaves above ground.
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