NCERT Solutions Class 8 Science Chapter 01 Exploring the Investigative World of Science

Question 1. What is the first step of scientific investigation?
Answer: Asking a question.
In simple words: The first thing you do in science is ask a question about something you wonder about.

Exam Tip: Remember that curiosity and questions are the foundation of all scientific work - examiners often ask what starts scientific thinking.

Question 2. What makes a puri puff up?
Answer: Steam inside the dough.
In simple words: When water in the dough gets hot, it turns into steam. This steam gets trapped and makes the puri blow up like a balloon.

Exam Tip: This is a key example of how heat changes water into gas - be ready to explain it with the water-to-steam change.

Question 3. Name the two effects of electric current.
Answer: Heating effect and magnetic effect.
In simple words: Electric current can make things hot, and it can also create a magnet. These are the two main ways it works.

Exam Tip: Both effects are important - the heating effect powers heaters and bulbs, while the magnetic effect runs motors.

Question 4. What kind of organisms are found in a drop of dirty water?
Answer: Microorganisms.
In simple words: Tiny living things too small to see with your eyes live in dirty water. You need a microscope to see them.

Exam Tip: Always mention that these are living things, even though they are so small we cannot see them without magnification.

Question 5. What is used to improve our eyesight?
Answer: Lenses.
In simple words: Lenses bend light to help our eyes focus better and see things more clearly.

Exam Tip: Explain that lenses are found in glasses, cameras, and microscopes - they all help with seeing.

Question 6. Which natural force helps bring a ball back to the ground?
Answer: Gravity.
In simple words: Gravity is the force that pulls things toward the Earth and makes them fall down.

Exam Tip: Gravity is always pulling downward - remember this force acts on everything around us all the time.

Question 7. Which gas helps in breathing?
Answer: Oxygen.
In simple words: Oxygen is the gas we breathe in from the air. Our body needs it to stay alive.

Exam Tip: Oxygen comes from the air and plants produce it - mention that we breathe it in and our cells use it for energy.

Question 8. What is the Moon's appearance change called?
Answer: Phases of the Moon.
In simple words: The Moon looks different shapes at different times - sometimes it is full, sometimes it is half, sometimes it is just a thin line.

Exam Tip: The Moon does not really change shape - it just looks different as the Sun lights up different parts of it from our view on Earth.

Question 9. Name one simple scientific tool used in experiments.
Answer: Thermometer.
In simple words: A thermometer is a tool that tells us how hot or cold something is.

Exam Tip: Know other tools too - ruler, scale, beaker, and flask are all common scientific tools.

Question 10. What type of matter allows particles to move freely?
Answer: Gas.
In simple words: In a gas, the tiny bits (particles) are not stuck together. They move around quickly and spread out in all directions.

Exam Tip: Compare the three states - in solids particles are packed tight, in liquids they slide past each other, but in gases they are free to roam.

Question 11. What does a calendar help us measure?
Answer: Time.
In simple words: A calendar shows us days, weeks, and months so we can keep track of when things happen.

Exam Tip: Calendars come from the Moon's phases - early humans used the Moon to know when to plant crops and hunt.

Question 12. What is the bending of light called?
Answer: Refraction.
In simple words: When light passes through something like glass or water, it bends and changes direction.

Exam Tip: A spoon in water looks broken because light bends as it passes through the water - this is refraction at work.

Question 13. What kind of surface reflects light well?
Answer: Smooth surface.
In simple words: Light bounces back nicely from flat, polished surfaces like mirrors. Bumpy surfaces scatter the light in many ways.

Exam Tip: Smooth surfaces give clear reflections, while rough surfaces spread light out - this is why mirrors must be smooth.

Question 14. Name one harmful effect of human activity on Earth.
Answer: Climate change.
In simple words: When people burn fuel and cut down trees, it makes the Earth warmer and changes our weather in bad ways.

Exam Tip: Climate change leads to hotter temperatures, more floods, and storms - connect it to pollution and greenhouse gases.

Question 15. What is a mixture?
Answer: A combination of two or more substances.
In simple words: A mixture is when you put two or more different things together. They stay separate and do not stick chemically.

Exam Tip: Air is a mixture of gases, and tea with sugar is a mixture - the key point is that the parts do not chemically join.

Question 16. What is the importance of curiosity in science?
Answer: Curiosity leads us to ask questions about things we see every day and to find answers by watching and investigating. It is the start of becoming a real scientist.
In simple words: When you feel curious about something, you ask questions and search for answers. That is how science happens.

Exam Tip: Examiners reward clear explanation of how curiosity drives investigation - link it to asking focused questions, not just random wondering.

Question 17. How does a puri puff up while frying?
Answer: Water in the dough transforms into steam when heat is applied. The steam becomes trapped inside, causing the puri to expand like a balloon.
In simple words: Heat turns the water in the dough into steam. The steam pushes outward and puffs up the puri.

Exam Tip: This is a classic example of phase change - water to steam - and gas expansion. Link it to physical change, not chemical.

Question 18. What are microorganisms and why are they important?
Answer: Microorganisms are very small living things present in water, air and soil. Some help our body break down food and are used to make medicines, but others lead to sickness and disease.
In simple words: Microorganisms are tiny living creatures. Some help us stay healthy, but some make us sick.

Exam Tip: Give examples - bacteria in yogurt are good, but germs that cause colds are bad - this balance is important to mention.

Question 19. How do vaccines help us stay healthy?
Answer: Vaccines prepare our body's defenses to recognize and fight harmful microbes. They teach our immune system to respond quickly to specific diseases, keeping us safe from serious illness.
In simple words: Vaccines teach your body how to fight germs. So when real germs come, your body already knows what to do.

Exam Tip: Use the word "immunity" - vaccines build immunity, meaning your body becomes resistant to the disease.

Question 20. What is the heating effect of electric current?
Answer: When electricity flows through a wire or conductor, it creates heat. This effect is used in many household items like electric irons, water heaters (geysers) and room heaters.
In simple words: Electric current makes things hot. That is why heaters and irons get warm when you turn them on.

Exam Tip: Mention the term "resistance" - the wire resists the flow of current and creates heat as a result.

Question 21. Explain force with an example.
Answer: A force is a push or pull that changes how an object moves. For instance, when you kick a football, you apply force to it, making it move across the ground.
In simple words: Force is a push or a pull. When you kick a ball, you push it with force, and it moves.

Exam Tip: Force always causes motion or stops motion - define it in terms of what it does, not just what it is.

Question 22. Why do cyclones occur?
Answer: Cyclones form because of a large gap in air pressure. Warm, wet air rises rapidly in low-pressure zones, and this creates strong winds and heavy rainfall around these areas.
In simple words: A cyclone happens when warm air rises fast. It creates very strong winds and lots of rain.

Exam Tip: Link pressure difference to air movement - air always moves from high pressure to low pressure, creating wind.

Question 23. What is the role of particles in states of matter?
Answer: In solids, particles are packed closely together and cannot move much. In liquids, particles are farther apart and can move past one another. In gases, particles are very far apart and move around freely in all directions. This movement of particles explains why each state of matter behaves differently.
In simple words: Particles are the tiny pieces that make up everything. How they move tells us if something is solid, liquid or gas.

Exam Tip: Always describe three states with particle movement in mind - tight packing means solid, loose means liquid, and very free means gas.

Question 24. How do mirrors and lenses help in daily life?
Answer: Mirrors bounce light and let us see our own image in them. Lenses bend light and are found in glasses, microscopes and cameras to help us see things more clearly and in more detail.
In simple words: Mirrors show you how you look. Lenses help you see small things bigger or faraway things closer.

Exam Tip: Give practical examples - bathroom mirror, eyeglasses, magnifying glass - so examiners see you understand real-world use.

Question 25. Why is Earth suitable for life?
Answer: Earth sits at just the right distance from the Sun, so it is not too hot and not too cold. It has water in its liquid form, and its atmosphere contains oxygen for breathing and shields us from harmful rays. All these conditions make life possible on Earth.
In simple words: Earth is just right for life. It has the right heat from the Sun, water to drink, air to breathe, and protection from bad sun rays.

Exam Tip: Always mention three things - right distance/temperature, liquid water, and protective atmosphere - to show you understand why Earth is special.

Question 26. Describe the steps involved in scientific investigation.
Answer:
1. Ask a focused question based on what you are curious about.
2. Plan a simple experiment to test your idea.
3. Change one thing at a time to see what happens.
4. Watch carefully and write down what you see.
5. Look at your results and reach a conclusion about what you learned.
In simple words: Science has steps - ask a question, do an experiment, check one thing at a time, watch carefully, and say what you found.

Exam Tip: The key word is "variable" - you must control and change only one variable at a time to know what caused the result.

Question 27. Explain how electric current is useful in our daily life.
Answer:
1. It gives us light through electric bulbs and lamps.
2. It warms water in geysers and cooks food in electric ovens and heaters.
3. It powers motors and machines through its magnetic effect.
4. It runs home appliances like ceiling fans, televisions and refrigerators.
In simple words: Electric current does many jobs - it lights up our homes, heats water, moves motors, and runs all our appliances.

Exam Tip: Remember the two effects - heating for warmth and light, magnetic for motion and machines - and give real examples of each.

Question 28. Write differences between elements, compounds and mixtures.
Answer:
Element: A pure substance made up of only one kind of atom (Example - Iron).
Compound: Two or more elements joined together through chemical bonds (Example - Water).
Mixture: Two or more substances joined together physically, not chemically (Example - Air).
In simple words: An element is one pure thing. A compound is two or more things chemically joined. A mixture is two or more things just put together but not chemically joined.

Exam Tip: The key difference is chemical vs physical combination - compounds have chemical bonds, mixtures do not.

Question 29. What are the different ways in which light behaves?
Answer:
1. Light bounces back from shiny, flat surfaces like mirrors (reflection).
2. Light bends and changes direction when it passes through lenses (refraction).
3. Rough surfaces spread light out in many directions instead of bouncing it back (scattering).
4. These properties are used in devices like eyeglasses, microscopes and mirrors to help us see.
In simple words: Light can bounce off mirrors, bend through glass, and spread out from rough things. These tricks help us see.

Exam Tip: Use the three behaviors - reflection, refraction, scattering - and connect each one to a real object or device students use.

Question 30. List the reasons why human activities are affecting the Earth's climate.
Answer:
1. Burning coal, oil and natural gas lets out greenhouse gases that trap heat in the air.
2. Cutting down forests reduces oxygen production and lets more CO₂ stay in the air.
3. Factory waste dirties the air and water, adding more pollution.
4. Using too many resources disturbs nature's balance and harms ecosystems.
In simple words: People burn fuel, cut trees, make waste and use too much. All of this makes Earth hotter and sicker.

Exam Tip: Connect each human action to its climate effect - burning to greenhouse gases, deforestation to lost oxygen, waste to pollution.