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Exploration: Entering the World of Secondary Science – Class 9 Science notes, important questions and MCQs

NCERT Class 9 Science, chapter 1. Notes, key terms, important questions with answers and MCQs.

Chapter overview

Science is a way of finding out how the world works by asking questions, observing, testing ideas with fair experiments and sharing evidence.

The scientific method

Observe → ask a question → form a hypothesis → test it with an experiment → analyse data → conclude.
A fair test changes only one variable at a time and keeps others constant (controls).
Results must be repeatable by others.

Measurement and safety

SI units: metre (length), kilogram (mass), second (time), kelvin (temperature), ampere (current), mole (amount), candela (luminous intensity).
Record data in tables and show patterns with graphs.
Lab safety: wear goggles, never taste chemicals, add acid to water.

Key terms

Hypothesis: a testable explanation or prediction
Variable: a factor that can change in an experiment
Control: the setup kept unchanged for comparison

Formulas

7 SI base units: m, kg, s, K, A, mol, cd

Important questions with answers

What is a hypothesis? Give an example.2 marks

A hypothesis is a testable guess that explains an observation. Example: "Seeds need water to germinate", which can be tested by keeping some seeds wet and some dry.

What is a fair test? Explain with an example.3 marks

In a fair test only one variable is changed and all others are kept the same, so that any difference is due to that one variable. Example: to test whether sunlight affects plant growth, use the same plant type, soil, pot and water, and change only the amount of sunlight.

Describe the steps of the scientific method using the question "Does salt water freeze slower than tap water?"5 marks

(1) Observation and question: roads are salted in winter; does salt slow freezing? (2) Hypothesis: salt water takes longer to freeze. (3) Experiment: take two identical cups with equal water, add salt to one (independent variable), keep both in the same freezer (controlled variables) and check every 10 minutes (dependent variable: time to freeze). (4) Record observations in a table. (5) Conclusion: compare times; if salt water froze later, the hypothesis is supported. (6) Share results and repeat to make sure they are reliable.

Quick revision

Science is evidence-based and testable.
Fair test = change one variable.
SI unit of mass is kilogram.

Exam tips

In "design an experiment" answers, name the variable you change, what you measure and what you keep the same.
A single result is weak evidence; repeat and average.

Practice MCQs

The SI unit of length is
1. centimetre
2. kilometre
3. metre
4. foot
Show answer
Answer: (c) metre. Metre.
A testable prediction in science is a
1. law
2. fact
3. theory
4. hypothesis
Show answer
Answer: (d) hypothesis. Hypothesis.
In a fair test you change
1. only one variable
2. all variables
3. no variable
4. two variables
Show answer
Answer: (a) only one variable. Only one at a time.
The SI unit of temperature is
1. degree Celsius
2. kelvin
3. Fahrenheit
4. joule
Show answer
Answer: (b) kelvin. Kelvin.
The setup kept unchanged to compare results is the
1. control
2. variable
3. hypothesis
4. sample
Show answer
Answer: (a) control. Control.
Which is the correct order?
1. question → hypothesis → experiment
2. experiment → question → hypothesis
3. conclusion → experiment → question
4. hypothesis → question → result
Show answer
Answer: (a) question → hypothesis → experiment. Ask, predict, then test.
A student tests whether light affects plant growth. What must be kept the same?
1. water, soil and pot size
2. amount of light
3. plant height
4. the result
Show answer
Answer: (a) water, soil and pot size. Only light should change.
Why should an experiment be repeated?
1. to change the hypothesis
2. to avoid recording data
3. to use more chemicals
4. to make results reliable
Show answer
Answer: (d) to make results reliable. Repeats reduce chance errors.

All chapters of Class 9 Science

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.