PHYSICS SAMPLE PAPER CLASS12 (2021)

PHYSICS SAMPLE PAPER(1)-2020 

CLASS 12TH  PHYSICS

TIME 3:00Hrs            MAXIMUM  MARKS  70

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 MCQs of 1 mark each; Section B has two case based questions of 4 marks each  

 (4)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 answer questions of 5 marks each.

                                                  SECTION A

Q1 Write the SI unit of gyromagnetic ratio.


Q2 What is the electric potential due to an electric dipole at an equatorial point?


Q3 What is the value of angular momentum of electron in the second orbit of Bohr’s model of hydrogen atom?

Q4 Which semiconductors are preferred to make LED's?

Q5 Name the physical constant having unit Joule -sec

Q6 Define wattless current?

Q7 How infra-red rays are produced? 

Q8 Show on a graph the variation of resistivity with temperature for a typical metal(copper).

Q9. A converging lens of refractive index 1.5 is kept in a liquid medium having 1.33 refractive index. What is the nature of the lens ? 

Q10 What are the dimensions  of electric potential ? 

For question numbers 11, 12, 13 and 14, two statements are given-one labeled 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.

11.    Assertion (A):It is advantageous to transmit electric power at high voltage.

Reason (R): High voltage implies low  current.  

12.    Assertion (A): Induction brakes make use of eddy currents.

Reason (R) : Eddy currents oppose the relative motion.


13.    Assertion (A) : Electron in hydrogen atom is bound to the nucleus.

Reason (R) : The total energy of electron in an orbit of hydrogen atom is negative.

.

14.    Assertion (A) : n-type semiconductor is negatively charged.

Reason (R): The minority charge carriers in n-type semiconductor are electrons. 

   

                                                      SECTION-B

Questions 15 and 16 are case study based questions and are compulsory.

question. Each question carriers 1 mark.

Moving Coil Galvanometer

15. Moving coil galvanometer operates on Permanent Magnet Moving Coil (PMMC) mechanism and was designed by the scientist D'arsonval. Moving coil galvanometers are of two types

  1. Suspended coil

  2. Pivoted coil type or tangent https://lh6.googleusercontent.com/lAt_6ONAbkpmR5UjVKqS5YMgqu1cNxWFUycXlfSmZUzqBnoXIZq5gko-0aw0OmAUfYkGi5Y1MYFyPLhU299l3Iz9cwC8SJv5JovW3Qz51wGV2D3bKxRQpovpXJzHfLaN3cK7RVTed44q6qDzlAgalvanometer. https://lh5.googleusercontent.com/nDu4c_FrULY-3Ac5HxA11h1eyfbL0DUtthyEf9V5XETHs4gj9jm0GSb0Y3FOnvY7QTfPW4xmG3p6fs0UIcM8oqjCCWhUjRl1H4JRBID2-Wo_-I0hcgeZvKpXLtafjh-Y9_I6aliNV71KUypBag

https://lh3.googleusercontent.com/gAIJuPJI5qdfABpP1sGrmIpfI0npH_6VNQ4JITgGXlhsfN2yf0ATvoF6S732hNG57z0ld6CY5cvfEJGzPkg9owJv7mNrtSHynTUP5nUqIcY0EG9AH0utoQYJqm8Qzp5BAhpgbyd_Pc4Bf4_X1AIts working is based on the fact that when a current carrying coil is placed in a magnetic field, it experiences a torque. This torque tends to rotate the coil about its axis of suspension in such a way that the magnetic flux passing through the coil is maximum.

(i) A moving coil galvanometer is an instrument which

  1. is used to measure emf

  2. is used to measure potential difference

  3. is used to measure resistance

         d.    is a deflection instrument which gives a deflection when a  current flows through its coil

(ii) To make the field radial in a moving coil galvanometer,

  1. number of turns of coil is kept small

  2. magnet is taken in tho form of horse-shoe

  3. poles are of very strong magnets 

  4. poles are cylindrically cut

https://lh5.googleusercontent.com/you1z76B9arPtOHGYYwwn2F_E1C2uOEwHLBY5qqS8PM8AQFLoPbMwX8CmVh_5hAH17luGaGwEMiCR_LqDA2mjlyamqNDBns32Qatd0fwvoCTLtKFX8LV_gITOzYv6D81viCdkyyCdO1IBspiiw


  

(iii) In a moving coil galvanometer, having a coil of N-turns of area A and carrying current I is placed in a radial field of strength B.

The torque acting on the coil is

    (a) NA2B2     (b) NABI²

    (c) N2ABI    (d) NABI

(iv) To increase the current sensitivity of a moving coil galvanometer, we should decrease

  1. strength of magnet

  2. area of the coil

  3. number of turns in coil

  4. all the above.


16. It is a semiconductor light source that emits light when current flows through it.Electrons in the semiconductor recombine with electron holes,releasing energy in the form of photons.The colour of the light is determined by the energy required for electrons to cross the band gap of the semiconductor.White light is obtained by using multiple semiconductors or a layer of light-emitting phosphor on the semiconductor device. 

(i) A light emitting diode is a ……………..p-n junction


  1.  heavily doped

  2. Lightly doped

  3.  Both( a) and (b)

  4. None of these


    (ii) Which of the following materials can be used to produce infrared LED


  1. Si

  2. GaAs

  3. CdS

  4. PbS

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(iii) What is the bandwidth of the emitted light in an LED?

(a)1nm to 10nm

(b)10nm to 50nm

(c)50nm to 100nm

(d)100nm to 500nm


(iv)What should be the band gap of the semiconductors to be used as LED?

(a)0.5eV

(b)1eV

(c)1.5eV

(d)1.8eV

SECTION-C

All questions are compulsory. In case of internal choices, attempt any one.




17. The radii of curvature of the faces of double convex lens are 10 cm and 15 cm. If the focal length of the lens is 20 cm. Find the refractive index of the material of the lens.

                                                OR

A biconvex lens has a focal length 2/3 times the radius of curvature of either surface. Calculate the refractive index of lens mmaterial.


18. What is the emf induced in the coil of self inductance of 5 mH when current changes from 2A to 0A in 10 s?                                              

19.Derive an expression for the Ohm's law in vector form.

Define mobility.   

20. Define the term Current density  .Write its S.I. unit .It is a scalar or vector quantity?                        

21. What are the conditions to obtain coherent sources?

22.Calculate the (i) momentum and (ii) de-Broglie wavelength of the electrons accelerated through a potential difference of 54 V. https://lh6.googleusercontent.com/nU1_dEfTpkWN__fwYxMkO2guSshVr0Ejy1lQj-LNPawENUJ9xZHoFqNI9327dT0xLlfytsvQwY3mVvPmL1ZzUudy3YP8QNMP1GzQfkHf40JvH_Bavq4O2dV3zN2OKL51mLVKxYwLAf5vxkWkXA

23.Define Ionisation energy and ground state.

Given the value of the ground state energy of hydrogen atom is -13.6eV.Find out its K.E and P.E in the ground state.

https://lh6.googleusercontent.com/obQYfgqAUGxomR21SSZF6yASGjnxbRCrtOE9mCLyKV5FO9X3wokrcXtAX1HUsujNHd6TPKDB7PZYY_5DQaQHT7gV_JL2xVxqMLeYlEkKCDUkFAHMx9zEMjSC1eCDJb9klfdqS5VRuPElC7bS7A



24. Calculate the steady current through the 2 ohm resistor in the circuit shown in the figure. 


https://lh4.googleusercontent.com/pPNoMGZMdJoazIa8YIRv6lP-CNBagflSRYWmtB0PtWSBnSscBvhdt8nHKyfJ1-VZEW6MuZ2akWQXrdqOZVNf_3nXdeBEcqOU-UITsQsDck4my8zDyiS-x2m0rax1XGFOOSYSxQO-ODxU54i9JA

225.Distinguish between n-type and p-type 

sesemiconductors on the basis of energy level diagram.

.

SECTION-D

All questions are compulsory. In case of internal choices, attempt any one.

26.(a)Define magnetic dipole moment.

Derive an expression for torque acting on a current loop placed in the uniform magnetic field. 

27. A coil of inductance 0.5 H and resistance 100 ohm is connected to a 200 V, 50 s -1 a.c. source. Calculate:

  1. the maximum current in the coil.

  2. And power factor.

  1. A converging lens has a focal length of 10 cm in air. It is made of a material of refractive index 1.5.It is immersed in a liquid of refractive index 1.67. Calculate its new focal length.

                                          OR

The image obtained with a convex lens is erect and its length is four times the length of the object. If the focal length of the lens is 20 cm, calculate the object and image distance.   

29.(a)Define mass-defect .

      (b) Differentiate between nuclear fission and nuclear fission(any two points of difference).


30. (i) With the help of circuit diagrams, distinguish between forward biasing and reverse biasing of a p-n junction diode.

(ii) Draw V-/ characteristics of a p-n junction diode in (a) forward bias, (b) reverse bias.

Or

Differentiate metals ,conductors and insulators on the basis of energy bands by drawing proper energy level diagrams. 

      SECTION-E

All questions are compulsory. In case of internal choices, attempt any one.

31.

(i) State Gauss'Law. Derive an expression for electric field due to infinitely thin plane sheet.

    1. Show that the electric field between two thin infinite plane oppsitely charged  sheet is zero?

OR

Derive an expression for the capacitance of a parallel plate capacitor having plate area A and plate separation d filled with dielectric medium of dielectric constant K.


  Find (a) the equivalent capacitance of the https://lh6.googleusercontent.com/TH1w4dNgIQO5I-hk482jOJYTDc5dFBeCRC1GX15LqQxynRCqaF3LHnLA8HCjWYjGmiP1cjmqWtpRV-sHqFaSC3wDPXJ90UotsQ7OQgzGebuN6sw34SDbvsx5DotZPUKIGsK0qD92xj2v32aZvw network (b) the charge 

                               https://lh6.googleusercontent.com/Oskf8l53tdPZcQDLwrv8bwGPbwCIalaqPq0N5vte3RUP7gej8qlvzbbUI8Mnwal8COgOXiZFw_3fZZcledhMnquNfyX0If9gIyxxEhCRPpUkGSkhAIv8v5pebLZVJKVptycNo93AtwCHm6ReOA

c.  And energy stored.

                   


 32. (i) Using Biot-Savart's law, deduce an expression for the magnetic field at the centre of a circular current carrying loop.

    1. Draw the magnetic field lines due to a current carrying loop

    2. A straight wire carrying a current of 12 A is bent into a semi-circular arc of radius 2.0 cm as shown. What is the magnetic field B at O due to:

  1. https://lh5.googleusercontent.com/ATu8Db-0aJCWhoPD8ws41Czbb4DFfNA7--EjDkEJrD60Bx5mvMbau55OWCVsZqbQXSDLaezZ3-pzIlY8dxSoYm1uK2vt5MohBzKOSr0O3bxo87qFPY12tlXEcuU00JCdJklI3O7qFVKlznMqIAstraight segments?    https://lh6.googleusercontent.com/9n0e7oxfQrSp01wJG3kkLyuMMkXNXjDMzwnOWVIAgj2lhLuZreV_Q6bSMmvvE5YH-6SACoYp6bwk3Ov_P5zlW3rbNVw-jGuPF0G4BNi6Iwk_asyERAl7tuO1oey43sv3CtWjVdo8w-seR9QLbg

  2. the semi-circular arc?

https://lh6.googleusercontent.com/S5NuIFBye9Y1oEpZtBuuvjk4ZmqOTothVYo-9-Hq2PxDkUFw-fzd2mrBB863xWoqMs7LpDAyU4-8o-boVthrgjHbg__jTg6yseFiYTh2PICyuKjOmSQJLsVmn5pY9bMgZWI8QHSehfimrHCHcA  

                                                   OR

  1. Using Ampere's circuital law, obtain the expression for the magnetic field due to a toroid. (b) In what respect is a toroid different from a solenoid? (c) Draw and compare the pattern of the magnetic field lines in the two cases. 

Q33  (a)Draw a ray diagram to show the working of a Astronomical Telescope. Deduce an expression for the total magnification when the final image is formed at the near point.(b) In a compound microscope,an object is placed at a distance of 1.5 cm from the objective of focal length 1.25 cm. If the eyepiece has a focal length of 5 cm and the final image is formed at the near point. Estimate the magnifying power of the microscope.

                   OR

What is interference of light? Write the condition for sustained interference pattern on screen. What is the effect on the interference fringes to a Young's double slit experiment when:(a) the separation between the two slits is increased?(b) the width of the source-slit is decreased?(c)In a Young's double slit experiment monochromatic light is used with path difference is λ. The intensity of light at a point on the screen is k units. What is the intensity of light at a point where path difference is λ/3 ?


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