NCERT Solutions for Class 9 Science Exploration Chapter 1: Entering the World of Secondary Science
Very Short Answer Type Questions (1 Mark)
Q: What does the magnifying glass framing the page numbers of the textbook symbolise?
Answer: It symbolises careful observation — noticing patterns and paying attention to what might otherwise be missed.
Q: What does the compass framing the page numbers of the textbook remind us about?
Answer: It reminds us that exploration needs direction — choosing appropriate models, asking the right questions and knowing the limits of where our ideas apply.
Q: What are scientific models?
Answer: Scientific models are simplified ways of looking at real systems that focus only on what is most important for a given question.
Q: How is a moving car represented in a physics model?
Answer: A moving car is represented as a single point.
Q: How are atoms and molecules represented in chemistry models?
Answer: Atoms and molecules are drawn as spheres and bonds.
Q: How is the Earth treated as a model in earth science?
Answer: The Earth is treated as a smooth sphere layered into distinct regions.
Q: What does the symbol 'c' represent in science?
Answer: 'c' represents the speed of light.
Q: From which Latin word does the symbol 'c' (speed of light) originate, and what does it mean?
Answer: It comes from the Latin word celeritas, meaning speed.
Q: What is the exact defined value of the speed of light today?
Answer: 299,792,458 m/s.
Q: What is a 'law' in science?
Answer: A law describes a regular pattern observed in nature, often expressed using words or mathematical relationships.
Q: What is a 'theory' in science?
Answer: A theory provides an explanation of why certain patterns occur, based on evidence gathered over time.
Q: What are 'principles' in science?
Answer: Principles are broad ideas that help us make sense in a given situation.
Q: Name the Indian physicist featured in the 'Meet a Scientist' section of Chapter 1.
Answer: Meghnad Saha.
Q: What was the total fuel requirement (in kg) of the aircraft in the fuel miscalculation incident?
Answer: 22,300 kg.
Q: By how many litres was the aircraft short of fuel in the mid-flight incident?
Answer: About 15,000 litres.
Q: Approximately how many litres of air does a person breathe in one day? (As per Example 1.3)
Answer: About 10,000 litres.
Q: How many breaths does a person take per minute at rest?
Answer: About 12 to 15 breaths per minute.
Q: What is the approximate volume of air in one breath?
Answer: About 0.5 litre.
Q: How many minutes are there in a day, as used in the estimation in Example 1.3?
Answer: 1,440 minutes (60 × 24 = 1440).
Short Answer Type Questions (2–3 Marks)
Q: Why does building a scientific model involve making assumptions and deliberately ignoring certain details?
Answer: The natural world is complex and studying it in full detail is often impossible. Scientific models deliberately ignore irrelevant details to keep things simple enough, yet still allow us to find answers to what we are looking for. These are purposeful choices, not mistakes.
Q: In Example 1.1 (the cricket shot), what details would you keep and what would you ignore in a simple model to predict whether the ball crosses the boundary?
Answer:
- Keep: Mass of the ball, speed and direction in which it has been hit.
- Ignore (in a simple model): Brand of the bat, colour of the ball, amount of grass on the field, air resistance, spin of the ball and stitching of the threads at the seam.
Q: Why must scientific language be very specific and precise?
Answer: Scientific ideas must be communicated clearly and unambiguously. To allow scientists across the world to describe observations, compare results and build ideas together, science uses a shared language of specific terms, symbols and units. Everyday words like force, work, cell and reaction have very precise, specific meanings in science that are different from their common usage.
Q: What role does mathematics play in science, according to Chapter 1?
Answer: Mathematics is a language that helps scientists think more clearly about the world. An equation is not just a calculation tool – it is a compact statement about how certain things are related. Using mathematics in science means understanding the situation first, identifying relevant quantities and then using mathematical relationships to reason carefully, not just to find numerical answers.
Q: What is the difference between a scientific law, a theory and a principle? Give one example of each.
Answer:
- Law: Describes a regular pattern in nature using words or mathematical relationships. Example: Newton's laws of motion.
- Theory: Explains why those patterns occur, based on evidence gathered over time. Example: Atomic theory explains how molecules are formed.
- Principle: A broad idea that helps make sense of a given situation. Example: Principle of conservation of energy applied while climbing stairs.
Q: What approach did Meghnad Saha use to study stars and what did this simplification allow him to discover?
Answer: Meghnad Saha did not try to model every atom, every reaction, or every movement inside a star. Instead, he treated the matter in a star as a hot gas, ignored many complex processes and focused only on temperature, pressure, and how atoms formed ions. This simplification allowed him to explain how the colour of a star is deeply connected to its surface temperature.
Q: In Example 1.2, what types of questions should Meghna ask to make Varsha's rain prediction — “It will rain this afternoon because the clouds look dark” – scientifically testable?
Answer: Meghna should ask questions that look for measurable evidence and past patterns, such as:
- What was the condition of the sky when it rained the last time?
- What is the humidity today?
- Was humidity above 80 per cent the last time it rained?
- What is today's wind speed and direction?
- Is the temperature dropping the way it did before the recent rains?
Q: Why do weather forecasts sometimes go wrong?
Answer: Weather depends on many changing factors such as temperature, pressure, humidity and wind. Weather forecasts use measurements and models, but very tiny differences in initial conditions can grow over time and lead to something completely different. This is why forecasts are usually reliable for a few hours or a few days, but become less certain further into the future.
Q: How can the viral claim – “Food should not be eaten during an eclipse because it becomes harmful” – be disproved using simple scientific questions?
Answer: An eclipse is simply a play of shadows. By asking basic scientific questions — Does any physical change occur during an eclipse? Does the temperature change significantly? Does food go bad if left in a shadow? — one concludes that no physical, chemical or biological mechanism supports this claim. Disproof comes from asking simple, logical scientific questions.
Q: Why are standard SI units important in science and daily life?
Answer: Standard SI units ensure that measurements mean the same thing everywhere, allowing scientific results to be compared and ensuring fairness in trade and daily life. The airplane fuel incident in the chapter shows the danger of unit mix-ups — the aircraft ended up about 15,000 litres short because pounds per litre were used instead of kilograms per litre. Using SI units everywhere avoids such conversions and errors.
Q: What helpful strategy does Chapter 1 suggest for solving science problems and tackling new situations?
Answer: Chapter 1 suggests:
- First understand the situation being studied.
- Then identify the quantities that matter.
- Finally, make a rough estimate to check whether an answer makes sense.
Q: What does the chapter say about symbols used in science? Give two examples.
Answer: Scientific symbols often come from history and are based on international agreements, not necessarily abbreviations of convenience. For example:
- 'c' for speed of light comes from the Latin word celeritas (speed).
- m, v, F, I represent mass, velocity, force and electric current respectively, each associated with a defined unit.
Q: In the context of predictions, what happens when a scientific prediction does not match observation?
Answer: When predictions do not match observations, scientists do not reject ideas based on opinion or belief — they re-examine their assumptions, models or measurements. No scientific theory is ever final and none is beyond question. This openness to being corrected by evidence is what makes science reliable and drives further exploration.
Q: Why are the divisions of science into physics, chemistry, biology and earth science described as not independent of each other?
Answer: The natural world does not have such boundaries. These divisions are made only to help organise knowledge. Most real-world problems – such as understanding climate change, developing medicines or designing sustainable technologies – require ideas from several disciplines together. Science also connects naturally with mathematics, technology, arts and social sciences.
Q: Using the example of a mask from Chapter 1, explain how solving real-world problems requires knowledge from multiple branches of science.
Answer: Understanding how a mask works requires concepts from:
- Physics: Particle motion and electrostatic attraction.
- Chemistry: Properties of polymer fibres.
- Biology: Size and behaviour of viruses.
- Mathematics: Modelling airflow and filtration efficiency.
Long Answer Type Questions (5 Marks)
Q: Explain the concept of scientific models with examples from four different branches of science. Why is the deliberate ignoring of details in a model considered a strength and not a mistake?
Answer: The natural world is complex, and studying it in full detail is often impossible. To make sense of this complexity, science uses models — simplified ways of looking at real systems that focus only on what is most important for a given question.
Examples of models from different branches of science:
Building a model involves making assumptions and deliberately ignoring certain details. For example, when studying the motion of a falling object, air resistance may be neglected to understand the basic effect of gravity. These choices are not mistakes – they are done on purpose to keep things simple enough, yet still allow us to find answers to what we are looking for. As models are developed further, more details can be added for greater accuracy. Therefore, simplification in models is a purposeful tool of science, not a flaw.
Examples of models from different branches of science:
- Physics: A moving car may be represented as a single point. All its complex parts, shape, and structure are ignored because they are irrelevant when studying its motion.
- Chemistry: Atoms and molecules are drawn as spheres and bonds. This ignores the internal structure of atoms but helps in understanding how substances combine and react.
- Biology: Cells are shown as diagrams highlighting key parts. When studying how the heart pumps blood, many individual cells are ignored so that the organ can be understood as a functioning system.
- Earth Science: The Earth is treated as a smooth sphere layered into distinct regions. This simplification is useful when studying large-scale planetary behaviour.
Building a model involves making assumptions and deliberately ignoring certain details. For example, when studying the motion of a falling object, air resistance may be neglected to understand the basic effect of gravity. These choices are not mistakes – they are done on purpose to keep things simple enough, yet still allow us to find answers to what we are looking for. As models are developed further, more details can be added for greater accuracy. Therefore, simplification in models is a purposeful tool of science, not a flaw.
Q: Describe Meghnad Saha's contribution as mentioned in the chapter. What does his approach teach us about the value of simplification in science?
Answer:
About Meghnad Saha:
Meghnad Saha was an Indian physicist who studied the light emitted by stars. His work is featured in Chapter 1 as a powerful example of how scientific simplification leads to significant discoveries.
His Approach:
Science often begins by ignoring details. When Meghnad Saha studied light from stars, he did not try to model every atom, every reaction or every movement inside a star. Instead, he treated the matter in the star as a hot gas. He ignored many complex processes and focused only on temperature, pressure and how atoms formed ions.
His Discovery:
This simplification allowed him to explain how the colour of a star is deeply connected to its temperature. Stars that appear blue are hotter; stars that appear red are cooler.
What his approach teaches us:
Meghnad Saha was an Indian physicist who studied the light emitted by stars. His work is featured in Chapter 1 as a powerful example of how scientific simplification leads to significant discoveries.
His Approach:
Science often begins by ignoring details. When Meghnad Saha studied light from stars, he did not try to model every atom, every reaction or every movement inside a star. Instead, he treated the matter in the star as a hot gas. He ignored many complex processes and focused only on temperature, pressure and how atoms formed ions.
His Discovery:
This simplification allowed him to explain how the colour of a star is deeply connected to its temperature. Stars that appear blue are hotter; stars that appear red are cooler.
What his approach teaches us:
- Simplification is not a shortcut — it is a deliberate and powerful scientific tool.
- By reducing a complex system to its most essential features, scientists can uncover relationships that would otherwise be hidden.
- As confidence in the model grows, more details can be added step by step.
- Science does not require complete information to begin – it requires the wisdom to know what to focus on.
Q: What is the difference between a law, a theory and a principle in science? Explain each with an example. Is a scientific theory just a guess? Give reasons.
Answer: In the secondary stage of science, students come across three important types of scientific ideas – laws, theories and principles. Each has a specific meaning.
1. Law:
No. A scientific theory is not a guess or an untested idea. It is:
1. Law:
- A law describes a regular pattern observed in nature.
- It is often expressed using words or mathematical relationships.
- Example: Newton's laws of motion – they explain the jerk felt when a bus stops suddenly.
- A theory goes a step further and provides an explanation of why those patterns occur.
- It is usually based on evidence gathered and tested over time.
- Example: The atomic theory explains how molecules are formed.
- Principles are broad ideas that help us make sense in a given situation.
- Example: The principle of conservation of energy – applied, for instance, when climbing up stairs.
No. A scientific theory is not a guess or an untested idea. It is:
- An explanation based on careful testing and critical examination.
- Always open to improvement and revision when new evidence becomes available.
- Subject to change if new evidence demands it – but only based on evidence, never on opinion or belief.
Q: Explain the role of mathematics in science as described in Chapter 1. How is an equation more than just a calculation tool?
Answer: Chapter 1 explains that as students explore science more deeply, they will notice that it uses language in a very careful and precise way. Mathematics is one of the most important parts of this language.
Mathematics as a language, not a hurdle:
Mathematics as a language, not a hurdle:
- Mathematics in science is not meant to be a hurdle or obstacle.
- It is a language that helps us think more clearly about the world.
- Learning to use mathematics in science does not mean memorising equations.
- An equation is a compact statement about how certain things are related.
- Example: Describing motion using quantities like distance, time, and velocity allows us to answer questions about where an object will be at a later moment.
- Similarly, mathematical expressions are used to describe rates of chemical reactions, patterns of population growth, and changes in energy within a system.
- Mathematics becomes a powerful language for thinking, not just for finding numerical answers.
- If a student focuses on understanding the situation and the quantities involved, equations will begin to feel less like obstacles and more like helpful guides in their exploration of science.
Q: What is meant by 'scientific predictions'? How do predictions help drive further exploration – even when they fail? Use examples from Chapter 1.
Answer: Chapter 1 describes the ability to make predictions as one of the most remarkable strengths of science.
What are scientific predictions?
When predictions fail:
What are scientific predictions?
- When laws, theories and models are well established, they allow us to anticipate what will happen under new or different conditions.
- These predictions can be made before performing an experiment – and in many cases even when an experiment cannot be performed at all.
- Predictions are not guesses – they are reasoned expectations based on evidence and careful thinking.
- Using ideas about motion, we can predict how far a kicked football will travel.
- Using knowledge of chemical reactions, we can predict how much carbon dioxide will be produced; how soft a baked bread will be.
- Using biological principles, we can predict how one's breathing will change while running.
When predictions fail:
- Scientists do not reject ideas based on opinion or belief – only on evidence.
- When predictions do not match observations, scientists re-examine their assumptions, models, or measurements.
- Even the most successful scientific theories have limits and may fail when new conditions are explored or when measurements become more precise.
- Such failures are not a weakness of science – they are its greatest strength.
- No scientific theory is ever final and none is beyond question.
Q: Using Example 1.3 from the chapter, explain the process of scientific estimation. Why does the chapter say that science values careful reasoning perhaps much more than accurate calculations?
Answer: Chapter 1 introduces students to the important scientific skill of estimation — making reasonable approximate calculations to check whether an answer makes sense.
Example 1.3 – Estimating litres of air breathed in one day:
Why science values careful reasoning over accurate calculations:
Example 1.3 – Estimating litres of air breathed in one day:
- Step 1: Estimate number of breaths per minute - At rest, a person takes about 12–15 breaths per minute. Approximate value used: about 15 breaths per minute.
- Step 2: Calculate total breaths per day - There are 60 × 24 = 1,440 minutes in a day. Total breaths ≈ 18,000 – 22,000, roughly 20,000 breaths per day.
- Step 3: Estimate volume of one breath - It takes about 4–5 breaths to fill a typical rubber party balloon. When inflated, a balloon holds about 2 litres. Therefore, one breath ≈ 0.5 litre.
- Step 4: Calculate total volume - 20,000 breaths × 0.5 litre = 10,000 litres per day.
Why science values careful reasoning over accurate calculations:
- Exact values are not always necessary, especially in the early stages of reasoning.
- An approximate estimate is enough to tell us whether a result is reasonable or impossible.
- Learning to estimate helps build intuition, detect errors and develop confidence in thinking.
- The aim is not to find the exact number, but to check whether the answer makes sense.
- As the chapter states – “Science values careful reasoning perhaps much more than accurate calculations.”
Q: Describe the airplane fuel miscalculation incident mentioned in Chapter 1. What lesson does it teach about the use of standard units in science?
Answer: Chapter 1 presents a real incident to illustrate why standard units matter in science and everyday life.
The Incident:
Lessons from the incident:
The Incident:
- A passenger aircraft ran out of fuel mid-flight due to a mix-up in units.
- The flight needed 22,300 kg of fuel in total.
- However, the ground crew used the wrong unit – they calculated the fuel using pounds (lb) per litre as the density, instead of kilograms (kg) per litre.
- As a result, the aircraft was loaded with far less fuel than required.
- The aircraft was about 15,000 litres short of fuel.
- Luckily, the aircraft could glide to an emergency landing. The aircraft was damaged, but there were no casualties.
Lessons from the incident:
- Standard (SI) units are critical – they ensure that measurements mean the same thing to everyone, everywhere.
- Unit mix-ups can have serious real-world consequences – not just in science, but in aviation, medicine, engineering, and daily trade.
- Using SI units everywhere avoids conversions and errors.
- This also connects to everyday life – when we buy a kilogram of rice or vegetables, we expect it to mean the same amount everywhere, based on agreed international standards, not local objects or opinions.
Q: What does Chapter 1 tell us about science as a human activity? How does it grow and develop over time?
Answer: Chapter 1 closes with an important reminder about the true nature of science — that it is far more than facts, equations, or experiments.
Science as a human activity: Science is a human activity shaped by:
The self-correcting nature of science:
Science as a human activity: Science is a human activity shaped by:
- Curiosity – asking questions about the world.
- Creativity – imagining new explanations and models.
- Collaboration – working with others, sharing results.
- Careful questioning – testing ideas rigorously before accepting them.
The self-correcting nature of science:
- No scientific theory is ever final and none is beyond question.
- When predictions do not match observations, scientists re-examine assumptions, models, and measurements.
- This openness to being corrected by nature itself is what has allowed science to help us understand the world.
Q: How does Chapter 1 use the example of a solar eclipse to teach scientific thinking? What does it say about checking viral claims on social media?
Answer: Chapter 1 includes a 'Threads of Curiosity' box that applies scientific reasoning to a commonly circulated belief about solar eclipses.
The Viral Claim: “Food should not be eaten during an eclipse because it becomes harmful”. This claim circulates widely on social media.
The Scientific Approach – asking simple questions: Rather than accepting or rejecting the claim based on belief, Chapter 1 shows how to disprove it using simple scientific questions:
Broader lesson: This example teaches students that scientific thinking is useful far beyond the classroom. It equips us to critically evaluate information we encounter in daily life, including on social media. Rather than accepting claims based on tradition or opinion, we should ask: What evidence supports this? What measurable, testable mechanism would explain it?
The Viral Claim: “Food should not be eaten during an eclipse because it becomes harmful”. This claim circulates widely on social media.
The Scientific Approach – asking simple questions: Rather than accepting or rejecting the claim based on belief, Chapter 1 shows how to disprove it using simple scientific questions:
- What physical change occurs during an eclipse? An eclipse is simply a play of shadows – the Moon comes between the Earth and the Sun, blocking sunlight temporarily.
- Does temperature change significantly during an eclipse? No significant change in temperature occurs.
- Does food go bad if it is left in a shadow? No – shadows do not cause any chemical or biological change in food.
Broader lesson: This example teaches students that scientific thinking is useful far beyond the classroom. It equips us to critically evaluate information we encounter in daily life, including on social media. Rather than accepting claims based on tradition or opinion, we should ask: What evidence supports this? What measurable, testable mechanism would explain it?