Class XI Physics NCERT Chapter 1

Class XI  :  NCERT Chapter 1

Q: What is Science?

Answer: Science is a systematic approach to understand natural phenomena in as much detail and depth as possible, and to use the knowledge so gained to predict, modify and control different phenomena.

Science is exploring, experimenting and predicting from what we see around us.

Q: What is the 'Scientific method'?

Answer: The scientific method involves several interconnected steps:

(a) Systematic Observation

(b) Controlled Experiments

(c) Qualitative and Quantitative Reasoning

(d) Mathematical Reasoning

(e) Prediction

(f) Verification or Falsification of theories


Remember:  To become acceptable, a scientific theory must be verified by relevant observations or experiments.


Q: What is Physics?

Answer:  Science has been divided into several categories like physics, chemistry, biology etc.

Exact definition of Physics is neither possible nor necessary.

A general idea is: In physics, we observe different natural phenomena and try to understand and explain why they happen. Then we want to deduce mathematical equations for each phenomenon. With the mathematical equations, we want to be able to predict about the phenomenon.

Q:  What are the two principal 'thrusts' in Physics?

Answer:  The two principal thrusts in physics are Unification, and, Reductionism.

Unification: Through unification, we attempt to explain diverse physical phenomena in terms of a few concepts and laws.

For example, the fall of an apple to the ground, and, the motion of the earth around the sun, are both explained using the same law, namely Newton's law of gravitation.

Reductionism: Reductionism means to study and explain a large and complex phenomenon by breaking it into many smaller parts; then studying these parts separately, along with their interactions with one another, to understand and explain the original large and complex phenomenon.

For example, consider the situation where a rotating ball falls through a liquid.

It can be broken down into two parts:

(a) fall of the ball through the liquid

(b) rotation of the ball in the liquid.

Both these parts are first studied separately, then combined to understand the fall of a rotating ball through a liquid.

Q: What are the different fundamental forces in nature?

Answer: There are 4 fundamentals forces in nature:

(i) Gravitational Force: It is the force of attraction between any two objects by virtue of their masses.

(ii) Electromagnetic Force: It is the force between charged particles.

(iii) Strong Nuclear Force: It is the force that binds protons and neutrons in a nucleus.

(iv) Weak Nuclear force: It appears in certain nuclear processes; e.g. in β decay.

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