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CBSE Sample Paper Class 12 Physics Set 7
SUBJECT: PHYSICS CLASS : XII
MAX. MARKS : 70 DURATION : 3 HRS
General Instruction:
(i) All questions are compulsory. There are 27 questions in all. (ii) This question paper has four sections : Section A, Section B, Section C and Section D. (iii) Section A contains five questions of one mark each, Section B contains seven questions of two marks each, Section C contains twelve questions of three marks each and Section D contains three questions of five marks each. (iv) There is no overall choice. However, an internal choice has been provided in one question of two marks, one question of three marks and all the three questions of five marks weightage. You have to attempt only one of the choices in such questions. (v) You may use the following values of physical constants wherever necessary : 8 34 19 7 1 0 12 2 1 2 31 9 2 2 0 0 27 27
Mass of neutron 1.675 10 , Mass of proton 1.673 10
e
c m s h Js e C TmA
C N m m kg Nm C
kg kg
23 23 1
Avogadro's number 6.023 10 per gram mole, Boltzmann constant 1.38 10 ^ JK
SECTION – A
Questions 1 to 5 carry 1 mark each.
1. For the same angle of incidence, the angle of refraction in two media A and B are 25^0 and 35^0 respectively. In which medium is the speed of light less? 2. Two metallic resistors are connected first in series and then in parallel across a d.c. supply. Plot of I – V graph is shown for the two cases. Which one represents a parallel combination of the resistors and why? 3. Write the function of a transducer in communication system. 4. The charging current for a capacitor is 0.25A. what is the displacement current across its plates? 5. A signal of 5KHz frequency is amplitude modulated on a career wave of frequency 2MHz. What are the frequencies of the side bands produced?
SECTION – B
Questions 6 to 12 carry 2 marks each.
6. Write the conditions for observing a rainbow. Show by drawing suitable diagram, to understand the formation of rainbow. 7. Out of the two magnetic materials ‘A’ has relative permeability slightly greater than unity while ‘B’ has less than unity. Identify the nature of the materials ‘A’ and ‘B’. Will their susceptibilities be positive or negative. 8. State the two Kirchhoff ’s rules used in electric networks. How are these rules justified? 9. Nichrome and copper wires of same length and area of cross section are connected in series, current is passed through them why does the nichrome wire get heated first? 10. The wavelength of photon and the de-Broglie wavelength of an electron have the same value. Show that energy of photon is (2 mc/h) times the kinetic energy of electron; where m, c and h have their usual meaning. 11. Given the value of the ground state energy of hydrogen atom as –13·6 eV, find out its kinetic and potential energy in the ground and second excited states. 12. The output of an OR gate is connected to both the inputs of an NAND gate. Draw the logic circuit of combination of gates and write its truth table. OR (i) Identify the logic gates marked P and Q in the given logic circuit.
(ii) Write down the output at X for the inputs A = 0, B = 0 and A = 1, B = 1.
SECTION – C
Questions 13 to 24 carry 3 marks each.
13. Two capacitors of capacitance 10 F and 20 F are connected in series with a 6 V battery.
After the capacitors are fully charged, a slab of dielectric constant (K) is inserted between the plates of the two capacitors. How will the following be affected after the slab is introduced : (a) the electric field energy stored in the capacitors (b) the charges on the two capacitors (c) the potential difference between the plates of the capacitors Justify your answer.
14. Use Biot-Savart law to derive the expression for the magnetic field on the axis of a current carrying circular loop of radius R. Draw the magnetic field due to a circular wire carrying current it. OR Derive an expression for the magnetic moment of an electron revolving around the nucleus in terms of its angular momentum. What is the direction of the magnetic moment of the electron with respect to its angular momentum?
23. (a) Distinguish between point to point and broadcast modes of communication. Give an example of each. (b) Explain the basic concept of mobile telephoning. 24. Describe the principle construction and working of a cyclotron. Explain why an electron cannot be accelerated using a cyclotron.
SECTION – D
Questions 25 to 27 carry 5 marks each.
25. With the proper circuit diagram show the biasing of a (i) npn transistor (ii) pnp transistor in common base configuration. Explain the movement of charge carriers through different part of the transistor. Hence show that IE = IC + IB. Why in a transistor, base is made thin and doped with little impurity atoms? Explain briefly. OR Draw the circuit diagram for npn transistor in common emitter configuration. With the help of typical output characteristics write the expressions for (i) input resistance (ii) output resistance and (iii) current amplification factor. When would you prefer to use a transistor as a common base or a common emitter amplifier? 26. (i) Draw a neat labelled diagram of a compound microscope. Explain briefly its working. (ii) Why must both the objective and the eyepiece of a compound microscope have short focal lengths? OR Describe Young’s double slit experiment to produce interference pattern due to a monochromatic source of light. Deduce the expression for the fringe width. In Young’s double slit experiment, the two ,slits are 0.03 cm apart and the screen is placed at a distance of 1.5m away from the slits, the distance between the central bright fringe and central bright fringe is 1 cm. Calculate the wavelength of light used. 27. A 2 F capacitor, 100 resistor and 8H inductor are connected in series with an AC source.
(i) What should be the frequency of the source such that current drawn in the circuit is maximum? What is the frequency called? (ii) If the peak value of emf of the source is 200V, find the maximum current. (iii) Draw the term ‘Sharpness of Resonance’. Under what condition, does a circuit become more selective? OR (i) With the help of a neat and labelled diagram, explain the principle and working of a moving coil galvanometer. (ii) What is the function of uniform radial field and how is it produced?
