Physics: Modern Physics: UPSC Previous Year Questions (Science and Technology)
1 previous year UPSC Prelims question on Physics: Modern Physics (Science and Technology). Choose an option to see the answer and explanation.
Explanations state facts as of the year each question was asked; words like “recently” refer to that year.
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UPSC 2001Science and Technology · Physics: Modern Physics
Q1. Consider the following statements: In a nuclear reactor, self-sustained chain reaction is possible, because: 1. more neutrons are released in each of the fission reactions. 2. The neutrons immediately take part in the fission process. 3. The fast neutrons are slowed down by graphite. 4. Every neutron released in the fission reaction initiates further fission. Which of these statements are correct?
Explanation
Nuclear fission is the process in which a heavy atomic nucleus, such as uranium-235 or plutonium-239, splits into two smaller nuclei, releasing a large amount of energy.
Statement 1 is correct: Each fission reaction releases multiple neutrons, which are crucial for sustaining the chain reaction.
Statement 2 is correct: The neutrons produced in fission reactions are used to initiate further fission events.
Statement 3 is correct: Graphite (a moderator) slows down fast neutrons, increasing the likelihood that they will cause further fission reactions, thus making reaction sustainable over longer periods.
Statement 4 is incorrect: Not every neutron released will necessarily cause further fission, as some neutrons may escape the reactor or fail to cause fission if not properly moderated.
Answer key for these questions
Q
UPSC year
Correct answer
1
2001
(a) 1, 2 and 3
Frequently asked questions
How many previous year UPSC questions are there on Physics: Modern Physics?
This page covers 1 previous year UPSC Prelims GS Paper-I questions on Physics: Modern Physics (Science and Technology), asked from 1996 to 2007. Each has the correct answer and an explanation.
How should I use previous year UPSC questions for Prelims?
Attempt each question first, then open the answer and read the explanation for every option. Repeat by chapter, and track which statements UPSC reuses across years. Previous year questions show the exam pattern and difficulty level.
Which years are covered for Physics: Modern Physics?
Questions on Physics: Modern Physics (Science and Technology) are available for 6 years, from 1996 to 2007. Use the Year filter to practise a single paper.
