## CBSE Class 11 Physics Sample Paper 2020-21

11 Physics

General Instructions:

(1) All questions are compulsory. There are 33 questions in all.

(2) This question paper has five sections Section A. Section B, Section C, Section D and Section E.

(3) Section A contains ten very short answer questions and four assertion reasoning of 1 mark each, Section B has two case based questions of 4 marks each, Section C contains nine short answer questions of 2 marks each,

Section D contains five short answer questions of 3 marks each and Section E contains three long answers questions of 5 marks each

(4) There is no overall choice. However internal choice is provided. You have to attempt only one of the choices in such questions.

SECTION A

- What is the cgs unit of pressure?
- State first law of thermodynamics.
- The velocities of three molecules are 3v, 4v and 5v. Calculate their root mean square velocity.
- What is the law of equi-partition of energy?
- Why the amplitude of the vibrating pendulum should be small?
- In the arrangement shown in the figure, the block of m is displaced, what is the frequency of oscillation?
- Two sound sources produce 12 beats in 4 seconds. By how much do those frequencies differ?
- Write any one factor on which the speed of sound depends.
- What do you mean by absolute error?
- Plot x-t graph for uniform motion.

For question numbers 11, 12, 13 and 14, two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.

(a) Both A and R are true and R is the correct explanation of A

(b) Both A and R are true but R is NOT the correct explanation of A

(c) A is true but R is false

(d) A is false and R is also false.

- Assertion. The dot product of one vector with another vector may be a scalar or a vector

Reason: If the product of two vectors is a vector then product is called a dot product. 12. Assertion: Frictional forces are conservative forces

Reason: Potential energy can be associated with frictional force

- Assertion Centripetal force does no work.

Reason: Force is always directed along the displacement

14: Assertion When a pendulum is made to oscillate on the surface of the Moon its time period increases.

Reason: Moon is much smaller as compared to earth.

SECTION B

- Force can also be described intuitively as a push or a pull. A force has both magnitude and direction, making it a vector quantity. It is measured in the SI unit of Newton and represented by the symbol F.The original form of Newton’s second law states that the net force acting upon an object is equal to the rate at which its momentum changes with time. If the mass of the object is constant, this law implies that the acceleration of an object is directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object.

(i) What is Newton’s second law?

(ii) Is momentum a vector quantity?

(iii) A force of5N acts on a body of weight 9.8 N. What is the acceleration produced in that body?

(iv)A ball of mass 0.2 kg moves with a velocity of 20 m/sec and it stops in 0.1 sec then what is the force on the ball.

- The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic processes, distinguishing two kinds of transfer of energy, as heat and as thermodynamic work, and relating them to a function of a body’s state, called Internal energy. The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but can be neither created nor destroyed.

(i) What is the SI unit of heat?

(ii) What do you mean by internal energy?

(iii) Heat given to a system is 35 joules and work done by the system is 15 joules. What will be the change in the internal energy of the system?

(iv) First law of thermodynamics is based on………….

SECTION C

- Derive an expression to find out relative error in a product.

OR

Prove that second equation of motion is correct by dimensional method.

- Define relative velocity

OR

The photograph of a house occupies an area of 175 cm on a 35 mm slide. The slide is projected on to a screen, and the area of the house on the screen is 1.55 m. What is the linear magnification of the projector screen arrangement?

- A monkey is descending from the branch of a tree with constant acceleration. If the breaking strength is 75% of the weight of the monkey, what is the minimum acceleration with which monkey can slide down without breaking the branch?

- Define sliding friction and static friction

- What is centre of mass?

OR

Derive 2^{nd} equation of motion by calculus method.

- What is gravitational potential energy at a point? much work is done in shifting a mass from the surface to a height equal to its radius?

- What is escape velocity? Derive an expression for the same.

- Explain the terms: Young’s modulus of elasticity and elastic fatigue.

- Define degree of freedom of a gas.

SECTION D

- The displacement (in metre) of a particle moving along x-axis is given by

x= 18 t +5 t2^{2}

Calculate:

(i) the instantaneous velocity at t= 2s,

(ii) average velocity between t = 2s and t=3s, and

(iii) instantaneous acceleration.

- State triangular law of vector addition. Show that resultant of two vectors A and B inclined at an angle 0 is

R AP.B + 2AB cos 0

- (i) What is meant by Simple Harmonic Motion (S.H.M)?

(ii) At what points is the energy entirely kinetic and potential in S.H.M?

(iii) What is the total distance travelled by a body executing S.H.M in a time equal to its time period, if its amplitude is A?

OR

Derive an expression for moment of inertia of a thin circular ring passing through the centre and perpendicular to the plane of the ring 92 State second law of thermodynamics.

- Define standing wave. Displacement of a string in which standing wave is formed is given as y (20 sin 157t cos 314 )

Find (a) Amplitude of individual waves (b) Velocity of wave.

OR

30 Explain in detail parallax method of measuring long distances,

SECTION E

V projectile is fired at an angle o with the horizontal (0) Show that its trajectory is a parabola

Obtain expressions for:

(ii) The maximum height attained.

(iv) The horizontal range:

(iii) The time of its flight and

(v) At what value of is the horizontal range maximum?

OR

An artificial satellite of mass 1000 kg revolves around the earth in circular orbit of radius 6500 km. Calculate

(1) Orbital velocity

(ii) Orbital kinetic energy

(ii) Gravitational potential energy Mass of the earth = 6 x 104 kg, G = 6.67 x 10″ Nm/kg’]

(iv) Total energy in the orbit.

Derive un expression for the velocity of the two masses m and m2, moving with speeds u and u undergoing

clastic collision in one dimension

OR

Define an adiabatic and isothermal process and state the conditions of their occurrence. Derive expressions for work done during above processes.

- State and prove Bernoulli’s theorem.

OR

What is thermal expansion? Explain in detail the types of thermal expansion. Derive a relation between all the three coefficients of thermal expansion for an isotropic body.