CMDLearn

Learn

Class 8 Science Ch 1, Exploring the Investigative World of Science: 8 practice questions with answers

CMDLearn ·

Here are 8 practice questions on Chapter 1 of the NCERT Class 8 Science book, Curiosity: Exploring the Investigative World of Science. Every question has a worked answer and the textbook page behind it. The chapter has no exercises of its own, so these questions practise what it teaches: reading the results of an investigation, planning how many runs a test needs, estimating something too big to count, reading the chapter's Chaitra calendar, and the ideas it previews for the rest of the year.

These questions are our own, drafted with AI help. Every number was re-computed by a script and every answer was checked against the chapter, but no practising teacher has reviewed them yet. If you find a mistake, please tell us.

For a walk through the chapter itself, with its puri investigation step by step and a self-check, see NCERT Class 8 Science Chapter 1 explained. The questions below are different ones.

What the chapter says you need

Facts from Chapter 1 of Curiosity (Reprint 2026-27, pages 1 to 7):

Reading and planning an investigation

Question 1. Neha's family tries the chapter's puri question at home: does the temperature of the oil change how fast a puri puffs? An adult does all the frying. Every circle of dough is the same thickness and goes into the oil the same way, and each oil temperature is tried twice. Here are the made-up times, in seconds, until each puri puffed: very hot oil 3 and 5; hot oil 6 and 6; not very hot oil 11 and 13. (a) What is the average time for each oil? (b) Which oil gave the fastest puff, and how many times longer did the slowest oil take? (c) Neha's brother says, "So thicker dough puffs more slowly." Can these results tell him that?

Answer: (a) 4, 6 and 12 seconds; (b) the very hot oil, and the not very hot oil took 3 times as long; (c) no. (a) (3 + 5) ÷ 2 = 4; (6 + 6) ÷ 2 = 6; (11 + 13) ÷ 2 = 12. (b) 12 ÷ 4 = 3. (c) Thickness was kept the same in every run, so these results say nothing about thickness. They only answer the question the family asked, about the oil. The chapter lists the things that can be changed, among them thickness and oil temperature, and testing thickness needs its own runs (page 6).

Question 2. The chapter says puris could be made with different flours (atta, maida) and fried in oil that is boiling hot, hot or not very hot (page 6). Arjun and his mother plan to try every flour with every oil temperature, and to repeat each pairing twice. An adult does all the frying. (a) How many puris must be fried? (b) If they also try three thicknesses of dough with every pairing, again twice each, how many then? (c) If each puri takes about 2 minutes, from rolling to writing down the result, how long would the plan in (b) take, in hours and minutes?

Answer: (a) 12; (b) 36; (c) 72 minutes, that is 1 hour 12 minutes. (a) 2 flours × 3 oil temperatures = 6 pairings, and 6 × 2 = 12. (b) 2 × 3 × 3 = 18 combinations, and 18 × 2 = 36. (c) 36 × 2 = 72 minutes, and 72 − 60 = 12, so 1 hour 12 minutes. Testing one more thing multiplied the work by three, one good reason to begin, as the chapter does, with a focused question (pages 2 and 6).

Question 3. The chapter's first page wonders which is larger: the number of sand grains on every beach and desert on Earth, or the number of stars in our galaxy. Nobody can count every grain, but you can estimate. Sana counts 250 grains in a pinch of sand that weighs 0.1 gram (made-up numbers). (a) About how many grains are in 1 kilogram of that sand? (b) In a 50 kg sack? (c) What is the idea behind her method?

Answer: (a) about 25,00,000 (25 lakh); (b) about 12,50,00,000 (12.5 crore); (c) count a small sample you can manage, then scale up. (a) 1 gram is 10 times 0.1 gram, so 250 × 10 = 2,500 grains per gram; 1 kg is 1,000 grams, so 2,500 × 1,000 = 25,00,000. (b) 25,00,000 × 50 = 12,50,00,000. (c) She measures something countable (one pinch) and multiplies, which works only if the pinch is like the rest of the sand. The chapter offers the sand-and-stars question as a starting point for curiosity, not as an exam question (page 1).

The chapter's calendar

Question 4. Page 5 of the chapter shows a calendar for the month of Chaitra, which runs from 22 March to 20 April 2025. Chaitra 1 falls on a Saturday, 22 March. (a) How many days does this Chaitra have? (b) On what date and day of the week does Chaitra 15 fall? (c) What does the chapter say watching the Moon's phases allowed people to do?

Answer: (a) 30 days; (b) Saturday, 5 April 2025; (c) make the first calendars. (a) 22 to 31 March is 10 days, and 1 to 20 April is 20 days: 10 + 20 = 30, which is also the last number on the calendar (page 5). (b) Chaitra 15 is 14 days after Chaitra 1. 14 days is exactly two weeks, so it is again a Saturday, and 22 March + 14 days = 5 April. (c) People who watched the Moon go through its phases again and again used that cycle to make the first calendars; later, sunrises, sunsets and the Moon's cycle were observed together, and many calendars grew from that (page 4).

The year ahead

Question 5. The chapter says we use electric current in two ways: its heating effect keeps us warm, and its magnetic effect helps motors run (page 3). Sort these into the two groups: an electric room heater, a ceiling fan, an electric kettle, a mixer-grinder, a washing machine, an electric iron for clothes.

Answer: heating effect: the room heater, the kettle and the electric iron; magnetic effect (they run on motors): the ceiling fan, the mixer-grinder and the washing machine. A heater, kettle or iron is useful because current makes it hot. A fan, mixer or washing machine is useful because a motor turns, and motors work through the magnetic effect (page 3). Chapter 4 of Curiosity covers both effects.

Question 6. The chapter sorts materials three ways (page 4): an element is a pure substance; a compound is made of two or more elements bonded together; a mixture is a combination you can separate by physical means. Sort these: (a) a copper wire; (b) water, which is hydrogen and oxygen joined together; (c) sugar stirred into tea; (d) sand with iron filings in it; (e) oxygen gas.

Answer: elements: (a) copper and (e) oxygen; compound: (b) water; mixtures: (c) sugar in tea and (d) sand with iron filings. Copper and oxygen are each a single pure substance. Water has two elements bonded together, so it is a compound. Sugar in tea and sand with iron filings can be separated by physical means (a magnet pulls the iron out of the sand), so they are mixtures; the chapter uses sugar dissolving in tea as its example of a solution (page 4).

Question 7. (a) According to the chapter, what decides whether moving air is a gentle breeze or a strong wind? (b) How does it say the particles in a solid and in a gas differ in how they move? (c) Why does it say we need to know about particles at all?

Answer: (a) the size of the difference in air pressure; (b) in a solid they cannot move much, in a gas they move around freely; (c) to explain, for example, how air pushes on things or why water boils at one particular temperature. (a) A small difference in pressure gives a gentle breeze, and a stronger difference gives strong winds and sometimes cyclones (page 3). (b) Everything is made of tiny particles; in solids they cannot move much, and in gases they can move around freely (page 4). (c) The chapter says that explaining air pressure, or the temperature at which water boils, means zooming in on the particles a material is made of and on how they move (page 4).

Question 8. The chapter's tour ends with what makes Earth "just right" for life (page 5). (a) What two things does it name as most important? (b) What does it say human activities can do, and with what result? (c) Which three ways of working does it say will help us protect the balance on which life depends?

Answer: (a) Earth's distance from the Sun, where water stays liquid, and an atmosphere that gives us oxygen and shields us from harmful ultraviolet rays; (b) cause small changes in Earth's temperature that disrupt climate patterns, with dangerous consequences; (c) observing, measuring and experimenting. All three are on page 5. The chapter adds that we humans cause the problem, and we are also the ones who must use science to solve it.

Practise Class 8 science

Where CMDLearn fits

CMDLearn is building an AI tutor for Classes 1 to 10 that explains a step and checks the child's working, but leaves the writing to the child. It is still in development, and no child uses it yet. If you would like to hear when there is something to try, you can join the waitlist.

Sources

All opened and read on 3 November 2026. Page numbers are the printed page numbers of the chapter (printed page = PDF page).

The facts are from the chapter above; the Chaitra calendar was read from the rendered page. The questions, the made-up figures and the worked answers are our own, and every number was re-computed by script. This guide is general information; follow your teacher and the textbook.

Practise this class: Class 8 worksheets, chapter by chapter · free practice, marked instantly