CLASS XI: PHYSICS : CHAPTER-1 : PHYSICAL WORLD

CLASS XI   |    PHYSICS    |    CHAPTER 1

      notes prepared by subhankar Karmakar

Q1. What is scientific method? Mention the various steps involved in it.

Ans. Scientific method: the step-by-step approach used by a scientist in studying natural phenomena and establishing laws which govern these phenomena is called scientific method. 

Generally, it involves the following steps:

a. Taking a large number of systematic observations by doing controlled experiments.

b. Studying these observations and making qualitative and quantitative reasoning.

c. Suggesting mathematical models to account for the observed behaviour.

d. Predicting new phenomena on the basis of suggested model.

e. Modifying the theory, if necessary, the light of fresh evidences.

Q2. Name the four basic forces in nature. Arrange them in the order of their increasing strengths.

Ans. Fundamental forces in nature: 

In the macroscopic world, we observe several kinds of forces. All the forces between microscopic objects arise from two fundamental forces:

a. Gravitational force(F_g) 

b. Electromagnetic force. (F_e)

In the microscopic world, there are two more basic forces:

c. Strong nuclear force(F_s)

d. Weak nuclear force (F_w)

(F_g) : (F_w) : (F_e) : (F_s) = 1: 10²⁵ : 10³⁶ : 10³⁸

Q3. Describe briefly the fundamental forces in nature.

Ans. There are four fundamental forces in nature. They are as follows:

a. Gravitational force(F_g) 

b. Electromagnetic force. (F_e)

c. Strong nuclear force(F_s)

d. Weak nuclear force (F_w)

Gravitational force(F_g) : it is a force of mutual attraction between two bodies by virtue of their masses. According to the Newton's law of gravitation, the gravitational attraction between two bodies of masses m₁ and m₂ separated by a distance r is given by

   F_g = Gm₁m₂/r²

Where G is the universal gravitational constant.

Electromagnetic force (F_e): 

The force acting between two electric charges at rest is called electrostatic force. Electrostatic force is a part of electromagnetic force. According to Coulomb's law, the magnitude of the electrostatic force (F_e) between two point charges q₁ and q₂ separated by a distance r in vacuum is given by

(F_e) = (1/4πεₒ).q₁q₂ / r²

Where εₒ is the permittivity of vacuum. 

The force acting between two magnetic poles is called magnetic force.

Together electrostatic force and magnetic force is known as electromagnetic force.

Weak nuclear force (F_w):

It is a force that appears only between elementary particles involved in a nuclear process such as the β-decay of a nucleus.  It is a short range force that operates only over the size of a nucleus (= 10⁻¹⁵ m)

Strong nuclear force(F_s):

The strong attractive force which binds together the protons and neutrons in a nucleus is called strong nuclear force. It is a short range force that operates only over the size of a nucleus (= 10⁻¹⁵ m)

Q4. What are the different conservation laws in Physics?

Ans. Conservation laws: in any physical process involving the different forces, some physical quantities, remain unchanged with time. Such quantities are called conserved quantities. The laws which govern the conservation of these quantities are called conservation laws.

There are four basic conservation laws:

a. Law of conservation of energy.

b. Law of conservation of linear momentum

c. Law of conservation of angular momentum

d. Law of conservation of charge.

Q5. Name the scientist who was first awarded two Nobel prizes.

Ans. Madame Marie Curie , for physics ine 1903 and for chemistry in 1911.

Q6. Who first discovered radioactivity?

Ans. A H Becquerrel in 1896.

Q7. Mention some important contributions of Albert Einstein to physics.

Ans. a. Mass energy equivalence

         b. Photoelectric effect

         c. Special theory of relativity

         d. General theory of relativity.

Q8. Name the Indian physicist who was first awarded the Nobel prize.

Ans. C V Raman.

Q9. What was the important discovery of CV Raman?

Ans. Inelastic scattering of light by molecules.

Q10. What was the major contribution of Indian physicist SN Bose?

Ans. Quantum statistics ( Bose Einstein statistics)

Q11. With which field work was the famous Indian physicist H J bhabha associated?

Ans. Cascade process in cosmic radiation.

Q12. Name the Indian physicist associated with the triple helical structure of proteins.

Ans. G N Ramachandran.

CLASS XI: PHYSICS : MOTION IN ONE DIMENSION : NUMERICALS

CLASS XI  |    PHYSICS    |    CHAPTER 3

      notes prepared by subhankar Karmakar

Q.1. A car is moving with a velocity 54 km per hour. It suddenly applied brake and comes to rest within 0.6 s. How much distance it will travel before it comes to rest?

Q2. A body travels a distance s₁ with velocity v₁ and distance s₂ with velocity v₂ in the same direction. Prove that the average velocity of the body

vₐ = {(s₁ + s₂)v₁v₂}/(s₁v₂ +  s₂v₁)

Q3. A car travels along a straight line for the first half time which speed 50 km/h and the second half time with speed 60 km/h. Find the average speed of the car.

Q4. On a foggy day, two driver spot each other when they are just 80m apart. They are travelling at 72 km/h and 54 km/h respectively. Both of them applied brakes retarding their cars at the rate of 5 m.s⁻². Determine whether they never collision or not.

Q5. A car accelerates from rest at a constant rate α for some time, after which it decelerates at a constant rate β to come to rest. If the total time elapsed is t second, then prove that

(i) the maximum velocity attained by the car

  Vₘₐₓ = (αβt)/(α + β)

(ii) the total distance travelled buy the car

  X  = (αβt²)/2(α + β)

Q6. A body covers 12 m in 2nd second and 20 m in 4th second. How much distance will it cover in 4 seconds after the 5th second?

Q7. Two buses A and B are at positions 50 m and 100 m from the origin at time t = 0. They start moving in the same direction simultaneously with uniform velocity of 10 m/s and 5 m/s. Determine the time and position at which A overtakes B. 

Q8.  A body covers a distance of 20 m in the 7th second and 24 m in the 9th second. How much shall it cover in 15th second?

Q9. An object is moving with uniform acceleration its velocity after 5 seconds is 25 m/s and after 8 seconds it is 34 m/s. Find the the distance travelled by the object in 12th second.

Q10. A ball thrown vertically upwards with a speed of 19.6 m/s from the top of a tower returns to the earth  in 6 second. Find the height of the tower. 

Q11. A ball is thrown vertically upwards with a velocity 20 m/s from the top of a multistoried building. The height of the point from where the ball is thrown is 25 m from the ground.

(a) How high will the ball rise? 

(b) How long will it be before the ball hits the ground?    (Take g = 10 m/s²)

Q12. Two balls are thrown simultaneously, A vertically upwards with a speed of 20 m/s from the ground, and B vertically downwards from a height of 40 m with the same speed and along the same line of motion. At what point do the two balls collide?