Option “3” is correct. Sun generates its energy by nuclear fusion of hydrogen nuclei into helium.
54. The half life of a radioactive substance is 10 day; it means there will be:
1. complete decay of substance in 20 days
2. complete decay of substance of 40 days
3. decay of ¾ part of substance in 20 days
4. decay of ¼ part of substance in 5 days
Option “3” is correct. The half life of a radioactive substance is 10 days; it means in next 10 days there will be half of the remaining radioactive substance. Thus, total 20 days, there will be decay of 75% or ¾ part of substance. [1/2+1/4=3/4]
55. At absolute temperature, the electric resistance in semiconductor is-
1. Infinite
2. Small
3. High
4. Zero
Option “1” is correct. The electrical conductivity of a semiconductor at absolute zero temperature is zero and they behave like an insulator. At this temperature the electric resistivity becomes infinite.
56. Which elements is the best conductor of electricity?
1. Silver
2. Copper
3. Alminium
4. Iron
Option “1” is correct. Electrical conductivity is a measure of the amount of electrical current under a material can carry. The most electrically conductive element is silver followed by copper, aluminium and iron.
57. The velocity of sound is maximum in-
1. Air
2. Liquid
3. Metal
4. Vacuum
Option “3” is correct. Velocity of sound is maximum in metal and minimum in gases.
Option “3” is correct. Hyetometer is the instrument used to measure rainfall.
59. Who established the foundations of the quantum theory?
1. Max Planck
2. Mark Nicholas
3. Albert Einstein
4. Alfred Hitchcock
Option “1” is correct. Max Planck was a German theoretical physicist, considered to be the initial founder of quantum theory, and one of the most important physicists of the 20th Century.
60. If in a motion, the axis of the rotation passes through an object, the motion is called _________.
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