The sample paper is one of the best resources for the student
to prepare for the exam. These help the student to get a prior experience
before they attempt for the final exam also, they will know if they are
prepared for the exam completely or not. They can test their knowledge for all
these subjects and get confident about the answer. if any discrepancies occur
in the written answer, they can focus more on such a question, so that there
are no mistakes happening in the final paper. they can also mark themselves for
correct and wrong answers.
Structure
of CBSE Class 12th Physics Model Paper 2020
Physics, the paper will
be of three hours and a total of 70 marks. the paper will consist of
37 questions in all divided into four sections. A, B, C, and D. All
questions are compulsory.
Section A:- There will be a total of 20 questions each question will have 1 mark.
Section B:- There will be a total of 7 questions each question will have 2 marks.
Section C:- There will be a total 7 question each question will have
3 marks.
Section D:- There will be a total three question each question will
have 5 marks.
There is no overall choice. However, internal choices have been provided in two questions of one mark each, two questions of two marks, one question of three marks and
three
questions of five marks weightage. You have to attempt only one of the choices in such questions.
You may use the following values of physical constants where ever necessary.
Section
– A
Directions (Q1-Q10) Select the most appropriate option from those given below each question
1.
A charge q is placed at the point of intersection of body diagonals of a cube. The electric flux passing through any one of its faces is.
2. The electric potential of the earth is taken to be zero because the earth is good.
(a)
Insulator (b) conductor (c) semiconductor (d) dielectric
3. If the ammeter in the given circuit shown in the diagram reads 2A, the resistance R is
(a) 1Ω (b) 2Ω (c) 3Ω (d) 4Ω
4. The heat produced by 100W heater in 2 minutes is equal to
(a) 10.5kJ (b) 16.3kJ (c) 12.0kJ (d) 14.2kJ.
5. The time period of a charged particle undergoing a circular motion in a uniform magnetic field is independent of
(a) speed of the particle (b) mass of the particle
(c) charge of the particle (d) magnetic field.
6. The final image formed in an astronomical refracting telescope with respect to the object is
(a) Real inverted (b) Real erect (c) Virtual erect (d) Virtual inverted
7. The shape of the interference fringes in Young’s double-slit experiment when D (distance between slit and screen) is very large as compared to fringe width is nearly
(a) straight line (b) parabolic (c) circular (d) hyperbolic
8. Polarized light is incident on a plane glass surface having refractive index √3The angle of incidence at which reflected and refracted rays would become perpendicular to each other is :
(a) 15° (b) 30° (c) 45° (d) 60°
9. Photoelectric emission from a given surface of the metal can take place when the value of a ‘physical quantity’ is less than the energy of the incident photon. The physical quantity is :
(a) Threshold frequency (b) Work function of surface
(c) Threshold wavelength (d) Stopping Potential
10. A photon beam of energy 12.1eV is an incident on a hydrogen atom. The orbit to which electron of H-atom be excited is
(a) 2nd (b) 3rd (c) 4th (d) 5th
Directions (Q11 –Q15) Fill in the blanks with an appropriate answer.
11. Horizontal and vertical components of the earth’s magnetic field at a place are equal. The angle of dip at that place is ________.
OR
A free-floating magnetic needle at North pole is __________to the surface of earth.
12. The magnetic flux linked with a coil changes by 2×10-2Wb when the current changes by 0.01A. The self-inductance of the coil is_______.
13. If the angular speed of the armature of a dynamo is doubled then the amplitude of the induced e.m.f will become_______.
14. An electron is accelerated through a potential difference of 100 V, then de-Broglie wavelength associated with it is approximately ____________Ao
15. An equilateral prism is made up of material of refractive index √3. The angle of minimum deviation of light passing through the prism is_________.
Directions (Q16 –Q20) Answer the following
16. Which physical quantity in a nuclear reaction is considered equivalent to the Q-value of the reaction?
17. Zener diode is used in reverse bias. When its reverse bias is increased, how does the thickness of the depletion layer change?
18. The initial concentration of a radioactive substance is No and its half-life is 12 hours. What will be its concentration after 36 hours?
19. The work function of Sodium is 2.75eV. What will be KE of the emitted electron when a photon of energy 3.54eV is incident on the surface of sodium?
20 From the information of energy band gaps of diodes, how do you decide which can be light-emitting diodes?
OR
Give anyone advantage of LEDs over conventional incandescent low power lamps
21. Derive the expression for drift velocity of a free electron in terms of relaxation time and the electric field applied across a conductor.
22. Find total energy stored in capacitors given in the circuit
23. An α - particle and a proton are accelerated through the same potential difference. Find the ratio (vα/ vp)of velocities acquired by two particles.
24. What is Brewster’s angle? Derive the relation between Brewster angle and refractive index of a medium which produces Plane Polarized light.
25. The work function of Cs is 2.14eV. Find
(a) threshold frequency for Cs
(b) The wavelength of incident light if the photocurrent is brought to zero by stopping the potential of 0.6 V.
26. Derive an expression for the radius of nth Bohr’s orbit in the Hydrogen atom.
OR
The energy of an electron in the first excited state in the Hydrogen atom is -3.4eV. Find KE and PE of electron
in the ground state.
27. Draw energy band diagram of p&n-type semiconductors. Also, write two differences between p and n-type semiconductors.
OR
The energy gap in a p – n photodiode is 2.8 eV. Can it detect a wavelength of 6000 nm? Justify your answer.
Section – C
28. State working principle of the potentiometer. Explain how the balance point shifts when the value of resistor R increases in the circuit of the potentiometer, given below.
29. Using Biot-Savart’s law, derive an expression for the magnetic field at any point on the axial line of a current-carrying circular loop. Hence, find the magnitude of magnetic field intensity at the center of the circular coil.
30. Obtain the resonant frequency and Q – factor of a series LCR circuit with L = 3H, C = 27𝛍F, R = 7.4Ω. It is desired to improve the sharpness of resonance of the circuit by reducing its full width at half maximum by a factor of 2. Suggest a.
31. State the conditions of total internal reflection. Refractive indices of the given prism material for Red, Blue and Green colors are respectively 1.39, 1.48 and
1.42 respectively. Trace the path of rays through the prism.
32. Define resolving power of an astronomical refracting telescope and write an expression for it in normal adjustment. Assume that light of the wave
length 6000Å is coming from a star, what is the limit of resolution of a telescope whose objective has a diameter of 2.54m?
OR
Write the basic assumptions used in the derivation of the lens – maker’s formula and hence derive this expression.
33. Show that 238U can not spontaneously emit a proton. Given:
92
34. Suggest an idea to convert a full-wave bridge rectifier to a half-wave rectifier by changing the connecting wire/s. Draw the diagram and explain your answer.
Section – D
35. (a) Using Gauss’s law, derive an expression for intensity of the electric field at any point near the infinitely long straight uniformly charged wire.
(b)The electric field components in the following figure are Ex = αx, Ey = 0, Ez= 0; in which α = 400 N/C m. Calculate
(i) the electric flux through the cube, and (ii)
the charge within the cube assumes that a = 0.1m.
OR
a) Define electrostatic potential at a point. Write its SI unit. Three charges q1, q2, and q3 are kept respectively at points A, B, and C as shown in figures. Write the expression for the electrostatic potential energy of the system.
b) Depict the equipotential surfaces due to
(i) an electric dipole
(ii) two identical negative charges separated by a small distance.
36. In the following diagram, the arm PQ of the rectangular conductor is moved from x = 0; outwards.
The uniform magnetic field is perpendicular to the plane and extends from x = 0 to x = b and
is zero for x >b. Only the arm PQ possesses substantial resistance ‘r’. consider the situation when the arm PQ
is pulled
outwards from x = 0 to x = 2b, and
is then moved back to x = 0 with constant speed ‘ѵ’. Obtain expressions for the (i) electric flux, (ii) the induced emf,(iii)the force necessary to pull the arm and (iv) the power dissipated as Joule heat.
Sketch the variation of these quantities with distance.
OR
Write the working principle of the cyclotron and with a suitable diagram to explain its working. Give any two applications of the cyclotron.
37. Derive mirror equation for a convex mirror. Using it, show that a convex mirror always produces a virtual image, independent of the location of the object.
OR
(a) Draw a ray diagram for the final image formed at distance of distinct vision (D) by a compound microscope and write an expression for its magnifying power.
(b) An angular magnification (magnifying power) of 30x is desired for a compound microscope using as the objective
of focal length 1.25cm and eyepiece of focal length 5cm. How will you set up the compound microscope?
