Chapter 1: Physical World
Physics XI : Complete NCERT Exercise Solutions
Master the fundamental concepts of physics with detailed solutions to all NCERT exercise questions. This chapter introduces the nature of physical laws, fundamental forces, and the scientific method.
Question 1.1
Albert Einstein once said: "The most incomprehensible thing about the world is that it is comprehensible." What do you think Einstein meant by this statement?
Answer & Explanation:
Einstein's statement reflects the wonder that the complex, vast universe can be understood through human-made laws, theories, and mathematics.
Key Interpretations:
• The universe operates under consistent, discoverable laws.
• Human mind, despite its limitations, can decode nature's patterns.
• The order in nature is not random—it follows principles that can be expressed mathematically.
• This "comprehensibility" is the foundation of science itself.
Example: Newton's law of gravitation explains both an apple falling and planetary motion using the same simple equation.
Key Interpretations:
• The universe operates under consistent, discoverable laws.
• Human mind, despite its limitations, can decode nature's patterns.
• The order in nature is not random—it follows principles that can be expressed mathematically.
• This "comprehensibility" is the foundation of science itself.
Example: Newton's law of gravitation explains both an apple falling and planetary motion using the same simple equation.
Question 1.2
"Every great physical theory starts as a heresy and ends as a dogma." Give examples from the history of science that validate this remark.
Answer & Explanation:
Meaning: New scientific ideas often face rejection (heresy) but once proven, become accepted truth (dogma).
Examples:
This reflects how science evolves through skepticism to acceptance.
Examples:
| Theory | Initial Rejection | Current Status |
|---|---|---|
| Heliocentric Model | Opposed by church and scholars | Foundation of astronomy |
| Quantum Mechanics | Rejected by classical physicists | Cornerstone of modern physics |
| Plate Tectonics | Ridiculed by geologists | Explains earthquakes and volcanoes |
| Germ Theory | Initially disputed | Foundation of modern medicine |
This reflects how science evolves through skepticism to acceptance.
Question 1.3
"Politics is the art of the possible. Similarly, Science is the art of the soluble." Explain this aphorism in the context of scientific practice.
Answer & Explanation:
Interpretation: Science focuses on problems that can be solved with available tools and methods.
Key Points:
• Scientists choose research questions that are solvable given current knowledge, technology, and methods.
• Not all mysteries are immediately addressable; science progresses by tackling soluble problems first.
• Example: Newton solved planetary motion with calculus and gravity; he didn't attempt to explain atomic structure (which required quantum mechanics later).
• This pragmatic approach ensures steady, incremental progress rather than futile pursuit of currently unsolvable questions.
Contrast with Politics: Politics seeks achievable compromises; science seeks achievable solutions.
Key Points:
• Scientists choose research questions that are solvable given current knowledge, technology, and methods.
• Not all mysteries are immediately addressable; science progresses by tackling soluble problems first.
• Example: Newton solved planetary motion with calculus and gravity; he didn't attempt to explain atomic structure (which required quantum mechanics later).
• This pragmatic approach ensures steady, incremental progress rather than futile pursuit of currently unsolvable questions.
Contrast with Politics: Politics seeks achievable compromises; science seeks achievable solutions.
Question 1.4
India has a large base in science and technology but hasn't yet realized its full potential as a world leader. What factors have hindered the advancement of science in India?
Answer & Explanation:
Factors hindering scientific advancement in India:
• Insufficient R&D Funding: Low investment compared to GDP.
• Brain Drain: Talented scientists migrate abroad for better opportunities.
• Bureaucratic Hurdles: Slow processes in grants, approvals, and research implementation.
• Education System: Rote learning over creativity and critical thinking.
• Infrastructure Gaps: Lack of advanced labs, equipment, and digital resources in many institutions.
• Industry-Academia Disconnect: Limited collaboration for applied research.
• Sociocultural Factors: Traditional mindsets sometimes resist innovative, evidence-based thinking.
Positive Steps: ISRO, DRDO, and initiatives like Atal Innovation Mission show potential for growth.
• Insufficient R&D Funding: Low investment compared to GDP.
• Brain Drain: Talented scientists migrate abroad for better opportunities.
• Bureaucratic Hurdles: Slow processes in grants, approvals, and research implementation.
• Education System: Rote learning over creativity and critical thinking.
• Infrastructure Gaps: Lack of advanced labs, equipment, and digital resources in many institutions.
• Industry-Academia Disconnect: Limited collaboration for applied research.
• Sociocultural Factors: Traditional mindsets sometimes resist innovative, evidence-based thinking.
Positive Steps: ISRO, DRDO, and initiatives like Atal Innovation Mission show potential for growth.
Question 1.5
No physicist has ever "seen" an electron, yet all believe in its existence. A superstitious person uses this to argue that ghosts exist even though unseen. How would you refute this argument?
Answer & Explanation:
Refutation: The analogy is flawed because scientific belief is based on evidence and predictability, not mere absence of visibility.
Electrons vs. Ghosts:
Key Point: Science demands testable evidence and reproducibility; superstition relies on anecdotes and faith.
Electrons vs. Ghosts:
| Electrons (Scientific) | Ghosts (Superstitious) |
|---|---|
| • Detected indirectly via instruments (cloud chamber, oscilloscope) | • No consistent, verifiable detection |
| • Predictable behavior (charge, mass, spin measured) | • No predictable properties or laws |
| • Theories involving electrons explain phenomena (electricity, chemistry) | • No explanatory power or testable theories |
| • Consensus across global scientific community | • Belief varies culturally, no empirical basis |
Key Point: Science demands testable evidence and reproducibility; superstition relies on anecdotes and faith.
Question 1.6
Crab shells in Japan resemble a Samurai's face. Two explanations: (a) supernatural tribute, (b) artificial selection. Which is scientific and why?
Answer & Explanation:
Scientific Explanation: (b) Artificial selection.
Why (b) is Scientific:
• Based on observable mechanism: fishermen releasing resembling shells.
• Leads to testable predictions: genetic propagation of the trait.
• Consistent with evolutionary biology: selection pressure changes population.
• No supernatural or unverifiable assumptions.
Why (a) is Unscientific:
• Invokes "inscrutable ways of nature" with no mechanism.
• Not testable, measurable, or reproducible.
• Relies on magical thinking rather than evidence.
Lesson: Scientific explanations are natural, mechanistic, and evidence-based.
Why (b) is Scientific:
• Based on observable mechanism: fishermen releasing resembling shells.
• Leads to testable predictions: genetic propagation of the trait.
• Consistent with evolutionary biology: selection pressure changes population.
• No supernatural or unverifiable assumptions.
Why (a) is Unscientific:
• Invokes "inscrutable ways of nature" with no mechanism.
• Not testable, measurable, or reproducible.
• Relies on magical thinking rather than evidence.
Lesson: Scientific explanations are natural, mechanistic, and evidence-based.
Question 1.7
What key scientific and technological advances triggered the Industrial Revolution in England and Western Europe?
Answer & Explanation:
Major Advances:
• Steam Engine (James Watt): Powered factories, railways, ships.
• Textile Machinery: Spinning jenny, power loom revolutionized cloth production.
• Iron and Steel Production: Bessemer process enabled strong, cheap metal for construction.
• Mechanization of Agriculture: Increased food supply, freeing labor for industries.
• Development of Railways and Canals: Improved transport of goods and raw materials.
• Advances in Chemistry: Fertilizers, dyes, and materials science.
• Electricity and Magnetism: Later stages saw generators, motors, telegraph.
These transformed society from agrarian to industrial, boosting economy and urbanization.
• Steam Engine (James Watt): Powered factories, railways, ships.
• Textile Machinery: Spinning jenny, power loom revolutionized cloth production.
• Iron and Steel Production: Bessemer process enabled strong, cheap metal for construction.
• Mechanization of Agriculture: Increased food supply, freeing labor for industries.
• Development of Railways and Canals: Improved transport of goods and raw materials.
• Advances in Chemistry: Fertilizers, dyes, and materials science.
• Electricity and Magnetism: Later stages saw generators, motors, telegraph.
These transformed society from agrarian to industrial, boosting economy and urbanization.
Question 1.8
The world is witnessing a "second industrial revolution." List key contemporary areas of science and technology driving this transformation.
Answer & Explanation:
Drivers of the Second Industrial Revolution:
• Information Technology: Computers, internet, cloud computing, big data.
• Artificial Intelligence & Machine Learning: Automation, decision-making systems.
• Biotechnology & Genetic Engineering: CRISPR, personalized medicine, GMOs.
• Nanotechnology: Materials with novel properties, medical applications.
• Renewable Energy Technologies: Solar cells, wind turbines, energy storage.
• Space Technology: Satellites, space exploration, GPS.
• Quantum Computing: Potential to solve problems beyond classical computers.
• Advanced Robotics: Manufacturing, surgery, service bots.
• Communications: 5G, fiber optics, global connectivity.
These are reshaping economy, healthcare, environment, and daily life.
• Information Technology: Computers, internet, cloud computing, big data.
• Artificial Intelligence & Machine Learning: Automation, decision-making systems.
• Biotechnology & Genetic Engineering: CRISPR, personalized medicine, GMOs.
• Nanotechnology: Materials with novel properties, medical applications.
• Renewable Energy Technologies: Solar cells, wind turbines, energy storage.
• Space Technology: Satellites, space exploration, GPS.
• Quantum Computing: Potential to solve problems beyond classical computers.
• Advanced Robotics: Manufacturing, surgery, service bots.
• Communications: 5G, fiber optics, global connectivity.
These are reshaping economy, healthcare, environment, and daily life.
Question 1.9
Write a short fiction piece (about 1000 words) speculating on science and technology in the 22nd century.
Answer & Explanation:
Note: This is a creative exercise. Below is an outline for a speculative fiction piece.
Title: "Echoes of Epsilon"
Setting: 22nd century Earth with interstellar colonies.
Key Technologies Imagined:
• Quantum Entanglement Communication: Instant messaging across light-years.
• Neural-Link Interfaces: Direct brain-to-internet connection for learning and work.
• Matter Replicators: 3D printing at molecular level for food, tools, organs.
• Anti-Aging Therapies: Gene editing and nanobots extending healthy lifespan to 150+ years.
• Dyson Swarms: Solar energy collectors around sun for near-limitless power.
• Terraforming: Making Mars and Europa habitable.
• AI Governance: Ethical AI systems managing resources and conflict resolution.
Plot Idea: A scientist on a distant colony discovers an ancient alien artifact that challenges humanity's understanding of physics, leading to a new unification theory of forces.
Theme: Balance between technological advancement and ethical responsibility.
Title: "Echoes of Epsilon"
Setting: 22nd century Earth with interstellar colonies.
Key Technologies Imagined:
• Quantum Entanglement Communication: Instant messaging across light-years.
• Neural-Link Interfaces: Direct brain-to-internet connection for learning and work.
• Matter Replicators: 3D printing at molecular level for food, tools, organs.
• Anti-Aging Therapies: Gene editing and nanobots extending healthy lifespan to 150+ years.
• Dyson Swarms: Solar energy collectors around sun for near-limitless power.
• Terraforming: Making Mars and Europa habitable.
• AI Governance: Ethical AI systems managing resources and conflict resolution.
Plot Idea: A scientist on a distant colony discovers an ancient alien artifact that challenges humanity's understanding of physics, leading to a new unification theory of forces.
Theme: Balance between technological advancement and ethical responsibility.
Question 1.10
Imagine you make a discovery with great academic interest but dangerous potential for society. How would you resolve this ethical dilemma?
Answer & Explanation:
Ethical Framework for Scientific Responsibility:
Steps to Resolve:
1. Assess Risks and Benefits: Objectively evaluate potential misuse vs. positive applications.
2. Consult Ethics Committees: Engage with institutional review boards, fellow scientists, ethicists.
3. Responsible Disclosure: Consider controlled publication, omitting sensitive details that enable weaponization.
4. Engage Policymakers: Work with governments to regulate the technology responsibly.
5. Public Engagement: Educate society about the discovery, fostering informed debate.
6. Whistleblowing: If risks are extreme and ignored, alert international bodies.
Examples from History: Atomic scientists (Manhattan Project) later advocated for nuclear disarmament. CRISPR inventors called for a moratorium on human germline editing.
Principle: Scientists have a moral duty to consider societal impact, not just academic pursuit.
Steps to Resolve:
1. Assess Risks and Benefits: Objectively evaluate potential misuse vs. positive applications.
2. Consult Ethics Committees: Engage with institutional review boards, fellow scientists, ethicists.
3. Responsible Disclosure: Consider controlled publication, omitting sensitive details that enable weaponization.
4. Engage Policymakers: Work with governments to regulate the technology responsibly.
5. Public Engagement: Educate society about the discovery, fostering informed debate.
6. Whistleblowing: If risks are extreme and ignored, alert international bodies.
Examples from History: Atomic scientists (Manhattan Project) later advocated for nuclear disarmament. CRISPR inventors called for a moratorium on human germline editing.
Principle: Scientists have a moral duty to consider societal impact, not just academic pursuit.
Question 1.11
Categorize these applications of science as good, bad, or ambiguous: (a) Smallpox vaccination, (b) Television, (c) Prenatal sex determination, (d) Computers, (e) Satellites, (f) Nuclear weapons, (g) Chemical/biological warfare, (h) Water purification, (i) Plastic surgery, (j) Cloning.
Answer & Explanation:
Categorization (with reasoning):
*Note: Prenatal diagnosis for genetic disorders is good; selective abortion based on sex is bad.
| Application | Category | Reason |
|---|---|---|
| (a) Smallpox vaccination | Good | Eradicated a deadly disease, saved millions. |
| (b) Television | Ambiguous | Can educate (good) or spread misinformation (bad). |
| (c) Prenatal sex determination | Bad* | Misused for female fœticide in some societies. |
| (d) Computers | Ambiguous | Boost productivity but can cause addiction, job loss. |
| (e) Satellites | Good | Weather forecast, communication, GPS, environmental monitoring. |
| (f) Nuclear weapons | Bad | Mass destruction, ethical concerns (though deterrence is debated). |
| (g) Chemical/biological warfare | Bad | Illegal, inhumane, indiscriminate harm. |
| (h) Water purification | Good | Prevents waterborne diseases, essential for health. |
| (i) Plastic surgery | Ambiguous | Can reconstruct burns (good) or promote unrealistic beauty standards (bad). |
| (j) Cloning | Ambiguous | Therapeutic cloning for organs (good), human reproductive cloning (ethical issues). |
*Note: Prenatal diagnosis for genetic disorders is good; selective abortion based on sex is bad.
Question 1.12
India has a tradition of scholarship yet also superstitious practices. How can science be used to counter such attitudes?
Answer & Explanation:
Strategies to Counter Superstition with Science:
• Education Reform: Teach scientific method, critical thinking from school level.
• Public Awareness Campaigns: Use media to explain natural phenomena (eclipses, comets) scientifically.
• Debunking Myths: Scientists and educators should address local superstitions with evidence.
• Promote Role Models: Highlight Indian scientists (C.V. Raman, Ramanujan, Kalam) as heroes.
• Community Engagement: Science fairs, planetariums, museum exhibits making science accessible.
• Legal Measures: Enforce laws against fraudulent "godmen" and dangerous practices.
• Encourage Curiosity: Replace fear with wonder—e.g., astronomy clubs to appreciate night sky, not fear it.
• Digital Literacy: Combat online misinformation with fact-checking resources.
Goal: Foster a culture that values evidence, inquiry, and rational thought.
• Education Reform: Teach scientific method, critical thinking from school level.
• Public Awareness Campaigns: Use media to explain natural phenomena (eclipses, comets) scientifically.
• Debunking Myths: Scientists and educators should address local superstitions with evidence.
• Promote Role Models: Highlight Indian scientists (C.V. Raman, Ramanujan, Kalam) as heroes.
• Community Engagement: Science fairs, planetariums, museum exhibits making science accessible.
• Legal Measures: Enforce laws against fraudulent "godmen" and dangerous practices.
• Encourage Curiosity: Replace fear with wonder—e.g., astronomy clubs to appreciate night sky, not fear it.
• Digital Literacy: Combat online misinformation with fact-checking resources.
Goal: Foster a culture that values evidence, inquiry, and rational thought.
Question 1.13
Despite legal equality, unscientific views about women's capabilities persist. Demolish these using scientific arguments and examples of great women.
Answer & Explanation:
Scientific Arguments Against Gender Bias:
• Neuroscience: No significant difference in cognitive abilities between genders; intelligence is individually varied.
• Genetics: Except for sex chromosomes, genetic makeup is similar; no "science" supports inferiority.
• Historical Evidence: Women have excelled when given opportunity.
Examples of Great Women in Science:
• Marie Curie: Only person with Nobel Prizes in two sciences (Physics & Chemistry).
• Rosalind Franklin: Crucial role in discovering DNA structure.
• Kalpana Chawla: First Indian-origin woman in space.
• Janaki Ammal: Renowned Indian botanist.
• Shakuntala Devi: "Human computer" mathematician.
• Kiran Mazumdar-Shaw: Pioneer in biotechnology.
Conclusion: Capability is individual, not gender-based. Equal opportunity leads to equal achievement.
• Neuroscience: No significant difference in cognitive abilities between genders; intelligence is individually varied.
• Genetics: Except for sex chromosomes, genetic makeup is similar; no "science" supports inferiority.
• Historical Evidence: Women have excelled when given opportunity.
Examples of Great Women in Science:
• Marie Curie: Only person with Nobel Prizes in two sciences (Physics & Chemistry).
• Rosalind Franklin: Crucial role in discovering DNA structure.
• Kalpana Chawla: First Indian-origin woman in space.
• Janaki Ammal: Renowned Indian botanist.
• Shakuntala Devi: "Human computer" mathematician.
• Kiran Mazumdar-Shaw: Pioneer in biotechnology.
Conclusion: Capability is individual, not gender-based. Equal opportunity leads to equal achievement.
Question 1.14
P.A.M. Dirac said: "It is more important to have beauty in the equations of physics than to have them agree with experiments." Criticize this statement and find beautiful equations in physics.
Answer & Explanation:
Criticism:
• Empirical Basis: Physics is grounded in observation; an equation that doesn't agree with experiments is simply wrong, no matter how beautiful.
• Beauty is Subjective: What is beautiful to one may not be to another; science requires objectivity.
• Historical Context: Dirac valued mathematical elegance, but his own work (Dirac equation) was later verified experimentally.
Balance: The ideal is both beauty and experimental agreement. Beauty can guide theory, but experiment is the final judge.
Examples of "Beautiful" Equations:
• E = mc² (Einstein) – simplicity, profound meaning.
• F = G m₁m₂/r² (Newton's gravitation) – universal, symmetric.
• Maxwell's Equations: Unify electricity, magnetism, light elegantly.
• Schrödinger Equation: Core of quantum mechanics, elegant wave formalism.
• Second Law of Thermodynamics: ΔS ≥ 0 – deep, time-asymmetric.
• Empirical Basis: Physics is grounded in observation; an equation that doesn't agree with experiments is simply wrong, no matter how beautiful.
• Beauty is Subjective: What is beautiful to one may not be to another; science requires objectivity.
• Historical Context: Dirac valued mathematical elegance, but his own work (Dirac equation) was later verified experimentally.
Balance: The ideal is both beauty and experimental agreement. Beauty can guide theory, but experiment is the final judge.
Examples of "Beautiful" Equations:
• E = mc² (Einstein) – simplicity, profound meaning.
• F = G m₁m₂/r² (Newton's gravitation) – universal, symmetric.
• Maxwell's Equations: Unify electricity, magnetism, light elegantly.
• Schrödinger Equation: Core of quantum mechanics, elegant wave formalism.
• Second Law of Thermodynamics: ΔS ≥ 0 – deep, time-asymmetric.
Question 1.15
Many physicists find great laws both simple and beautiful. Name physicists who expressed this and explore their writings.
Answer & Explanation:
Physicists Who Valued Simplicity and Beauty:
• Albert Einstein: "Everything should be made as simple as possible, but not simpler."
• Niels Bohr: Appreciated complementarity and symmetry in quantum theory.
• Werner Heisenberg: Saw beauty in matrix mechanics and uncertainty principle.
• S. Chandrasekhar: Wrote on beauty and aesthetics in scientific discovery.
• Richard Feynman: Celebrated elegance in nature's laws; his lectures are classics.
• Paul Dirac: As quoted, prioritized mathematical beauty.
Suggested Readings:
• Feynman's "Surely You're Joking, Mr. Feynman!"
• Chandrasekhar's "Truth and Beauty"
• Einstein's popular essays
• Bohr's philosophical writings
Their works inspire awe for nature's order and the joy of discovery.
• Albert Einstein: "Everything should be made as simple as possible, but not simpler."
• Niels Bohr: Appreciated complementarity and symmetry in quantum theory.
• Werner Heisenberg: Saw beauty in matrix mechanics and uncertainty principle.
• S. Chandrasekhar: Wrote on beauty and aesthetics in scientific discovery.
• Richard Feynman: Celebrated elegance in nature's laws; his lectures are classics.
• Paul Dirac: As quoted, prioritized mathematical beauty.
Suggested Readings:
• Feynman's "Surely You're Joking, Mr. Feynman!"
• Chandrasekhar's "Truth and Beauty"
• Einstein's popular essays
• Bohr's philosophical writings
Their works inspire awe for nature's order and the joy of discovery.
Question 1.16
The stereotype of scientists as dry, humorless introverts is false. Give examples of humorous, adventurous scientists and their contributions.
Answer & Explanation:
Scientists with Humor and Adventure:
• Richard Feynman: Played bongo drums, cracked safes at Los Alamos, wrote hilarious anecdotes. Nobel Prize in QED.
• George Gamow: Wrote popular science books ("Mr Tompkins" series), proposed Big Bang theory, playful approach to physics.
• Carl Sagan: Brought cosmic wonder to public through "Cosmos", poetic and engaging.
• Subrahmanyan Chandrasekhar: Deeply artistic, wrote literary criticism alongside astrophysics.
• Neil deGrasse Tyson: Modern science communicator with wit and charisma.
• Homi Bhabha: Painter, musician, founded India's nuclear program.
Takeaway: Science is a human endeavor filled with creativity, humor, and passion. Breaking stereotypes encourages more young people to pursue science.
• Richard Feynman: Played bongo drums, cracked safes at Los Alamos, wrote hilarious anecdotes. Nobel Prize in QED.
• George Gamow: Wrote popular science books ("Mr Tompkins" series), proposed Big Bang theory, playful approach to physics.
• Carl Sagan: Brought cosmic wonder to public through "Cosmos", poetic and engaging.
• Subrahmanyan Chandrasekhar: Deeply artistic, wrote literary criticism alongside astrophysics.
• Neil deGrasse Tyson: Modern science communicator with wit and charisma.
• Homi Bhabha: Painter, musician, founded India's nuclear program.
Takeaway: Science is a human endeavor filled with creativity, humor, and passion. Breaking stereotypes encourages more young people to pursue science.
📘 Exam Preparation Tip:
Through these exercises, students will develop a philosophical and practical understanding of physics as a discipline. They'll explore the scientific method, distinguish science from superstition, appreciate the history of scientific revolutions, and confront ethical dilemmas in research. The questions foster critical thinking about physics' role in society, gender equity in science, and the interplay between technology and human progress.