CBSE Class XII Model Paper of Physics (Model Papers) 2012

General instructions:

(i) All questions are compulsory.
(ii) There are 30 questions in total. Questions 1 to 8 carry one mark each, questions 9 to 18 carry two marks each, questions 19 to 27 carry 3 marks each and questions 28 to 30 carry 5 marks each.
(iii) There is no overall choice. However, an internal choice has been provided in one question of two marks, one question in 3 marks and all three questions of 5 marks each. You have to attempt only one of the given choice in such questions.
(iv) Use the calculators is not permitted.
(v) You may use the following physical contents wherever necessary:
c = 3 x 108 ms-1 h = 6.6 x 10-34 JS
e = 1.6 x 10-19 C me = 9.1 x 10-31 kg
μo = 4p x 10-7TmA-1
Boltzmann contant k = 1.38 x 1023JK-1
Avogadro’s number N = 6.023 x 1023 / mole
Mass of neutron mn = 1.6 x 10-27kg

Q.1 There are five balls 1,2,3,4 and 5. Balls (1,2), (3,4) and (2,5) attract each other whereas (1,4) and (3,5) show repulsion. What is the charge on ball 2?

Q.2 An electron passes through a region of crossed electric and magnetic fields of intensities E and B respectively. For what value of electron speed will the beam remain undeflected?

Q.3 What is the angle of dip at a place where the horizontal component is v3 time of the vertical component of earth magnetic field?

Q.4 If the earth did not have atmosphere would its average temperature be higher or lower than what is now?

Q.5 Why does the sky appear blue?

Q.6 how does the maximum kinetic energy of electrons emitted vary with the work function of the metal?

Q.7 Zener diodes have higher densities as compare to ordinary p-n junction diodes. How does it effect the width of depletion layer and junction field?

Q.8 Is the ratio of number of holds and the number of electrons in an n – type extrinsic semi conductor more than, less than or equal to 1?

Q. 9 Calculate the potential at the centre of square of side v4.5 m which carries at its four corners charges of 5 μc, 2 μc, – 5 μc and – 7 μc.

Q. 10 A potentiometer is being used for the determination of the internal resistance of a cell of emf E = 1.5 volt. The balancing point of the in open circuit is at 76.3 cm length of the potentiometer wire. When a resistor of 9.5 ohm is connected across the cell, the balance point shifts to 64.8 cm length of the wire. Find the internal resistance of the cell.

Q. 11 The voltage – current variation of two metallic wires X and Y at constant temperature are as show in figure. Assuming that the wires have a
larger resistivity and why?

Q.12 (a) Why does a metallic piece becomes very hot when it is surrounding by a coil carrying high frequency alternating current?
(b) Steel is preferred for making electromagnets. Give one reason.

Q.13 Electromagnetic radiations with wave length
(i) λ1 are used to kill germs in water purifiers
(ii) λ2 are used in TV communication system
(iii) λ3 play an important role in maintaining the earth’s warmth.
Name the part of the electro magnetic spectrum to which these radiations belong. Arrange these wavelength in decreasing order of there
magnitude.

Q.14 What the effect on the interference fringes in young’s double slit experiment, if
(i) The separation between the slits Is halved and
(ii) Entire apparatus is immersed in liquid of refractive index μ. And show the interference pattern on the screen.

Q.15 Why are photodiodes used preferable in reverse bias condition? A photodiode is fabricated from a semiconductor with band gap of 2.8 eV.
Can id detect a wave length of 6000 nm? Justify.
OR
Draw the circuit diagram of a full wave rectifier and briefly explain its working principle.

Q16 What does the term LOS communication mean? Name the types of waves that are used for this communication. Which of the two-height of transmitting antenna and height of receiving antenna can effect the range over which this mode of communication remains effective?

Q17 Derive the expression for the self inductance of a solenoid.

Q18 A series LCR circuit with R=20Ω, L=1.5H and C=35μf is connected to a variable frequency 200 volt ac supply. When the frequency of supply equals to the naturals frequency of the circuit, what is the average power transferred to the circuit in one complete cycle?

Q19 In the circuit figure E, F, G and H are cells of emf 2, 1, 3 and 1 volt and their internal resistances are 2, 1, 3 and 1Ω respectively. Calculate
(i) The potential difference between B and D
(ii) The potential difference across the terminals and each of the cells G and H.

Q20 Explain with the help of a neat and labelled diagram, the principle and working of a transformer. How eddy currents can be minimized in transformer?

Q21 (a) Draw a neat labeled diagram of compound microscope.
(b) How does resolving power of compound microscope change on
(i) Decreasing the wave length of light use and.
(ii) Decreasing the diameter of objective lens.

Q22 (a) Derive and expression for the width of the central maxima for diffraction of light at a single slit.
(b) What two main changes in diffraction pattern of a single slit will you observe, when monochromatic source of light is replaces by a source of white light.
Q23 (a) Derive an expression for the de-Broglie wave length associated with and electron accelerates from rest through a potential difference V.
(b) Calculate the momentum of electrons, if their wavelength is 2Ao.

Q24 A neutron is absorbed by a 3Li6 nucleus with the subsequent emission of an alpha particle.
(i) write the corresponding nuclear reaction.
(ii) Calculate energy released in mev in this reaction.
Given: mass 3Li6= 6.01512126u, mass(neutron)=1.0086654u
Mass (alpha particle)=4.0026044u, mass (triton)=3.0100000u.
Take 1u=931 mev/c2

Q25 (a) State any two Bohr postulates for hydrogen atom.
(b) The sequence of step wise decays of radio active nucleus is

If the nucleon number and atomic number for D2 are respectively 176 and 71, what are the corresponding values for D and D4 nuclei. Justify your answers.

Q26 Draw a leveled circuit diagram of a common emitter amplifier using n-p-n transistor. Define the term trans-conductance and write it an expression for it. Draw output and input wave from
OR
(a) What do you understand by truth table of a logic gate?
(b) The two input A and B are inverted by using two NOT gates and their outputs are fed to the NOR fates as shown in figure

Analyse the action of fates (1) and (2) and identify the logic gate of the complete circuit so obtained. Give its symbol and the truth table.

Q27 Explain, why high frequency carrier waves are needed for effective transmission of signals.
A message signal of 12 kHz and peak voltage 20V is used to modulate a carrier wave of frequency 12 MHz and peak voltage 30V. Calculate the (i) Modulation index (ii) side band frequencies.

Q28 (a) Give the principle of working of Vande Graff generator.
(b) In the given network, find the charge on each capacitor.
(i) when the key K1 is closed.
(ii) when both K1 and K2 are closed.
Tabe C1 = 1μF C2=2μF, C3=3μF and C4 = 4μF

OR
(a) Using Gauss’s law derive an expression for the electric field intensity at any point outside a uniform charged thin spherical shell of radius R and charge density σCm-2. Draw the filled line when the charge density of sphere is (i) positive (ii) negative.
(b) Calculate the work done to dissociate the system of three charges placed on the vertices of a triangle as shown in figure. Take q=1.6X10-10 C.

Q.29. With the help of a neat labelled diagram explain the principle and working of moving coil galvanometer. What is the function of (i) Uniform radial field (ii) Soft iron core in such device.
OR
(i) Using Biot Savart law derive an expression for magnetic field due to a current carrying loop at a point along the axis of loop.
(ii) A long straight wire of a circular cross section of radius ‘r’ carrying study current I which is uniformly distributed across this cross section. Calculate the magnetic field in region R>r and R

Q.30 (a) Using the relation for refraction at a single spherical refracting surface derive the lens maker formula.
(b) Aconvex lens of focal length 0.2 m and made of glass (μ=1.50) is immersed in water (μ=1.33). Find the change in focal length of the lens.
(c) How is the focal length of a spherical mirror affected, when the wave length of the light used is increased ?
OR
(a) Using Huygen’s principle explain the refraction of a plane wave front at a plane surface.
Hence prove Snell’s law.
(b) Write to conditions of total internal reflection.
(c) An object is placed in front of a convex mirror of focal length 30 cm. if the image formed is quarter of the size of object. Find the
position of the image.

TIPS

1. 1. Draw all ray diagram and electric circuits by HB pencil.
2. 2. Underline the main points in theoretical questions.
3. 3. All the digits in numerical should be distinguishable, do not overwrite in the digits.
4. 4. Take care of time management.
5. 5. Complete the question paper at least 10 minutes before.

By:- Amar Ujala

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δ=?
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δ= tan’1(Bv/Bh)
= tan’1(1/√3)
=tan’1(tan 30)
therefore , δ= 30 degree

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• Q.29. With the help of a neat labelled diagram explain the principle and working of moving coil galvanometer. What is the function of (i) Uniform radial field (ii) Soft iron core in such device.
OR
(i) Using Biot Savart law derive an expression for magnetic field due to a current carrying loop at a point along the axis of loop.
(ii) A long straight wire of a circular cross section of radius ‘r’ carrying study current I which is uniformly distributed across this cross section. Calculate the magnetic field in region R>r and R

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• Q22 (a) Derive and expression for the width of the central maxima for diffraction of light at a single slit.
(b) What two main changes in diffraction pattern of a single slit will you observe, when monochromatic source of light is replaces by a source of white light.

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