THE INDIAN COMMUNITY SCHOOL, KUWAIT SECOND SEMESTER EXAMINATION PHYSICS (Theory)

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1 CLASS:XII Marks : 70 General Instructions: THE INDIAN COMMUNITY SCHOOL, KUWAIT SECOND SEMESTER EXAMINATION PHYSICS (Theory) Time : Hrs (i) (ii) (iii) (iv) (v) All questions are compulsory. This question paper has five sections: section A, Section B, Section C, Section D and Section E. Section A contains five questions of one mark each, section B contains five questions of two marks each, Section C contains twelve questions of marks each, Section D contains one value based question of four marks and section E contains three questions of five marks each. There is no overall choice. However, an internal choice has been provided in questions of two marks, one question of three marks and all three questions of five marks weightage. You have to attend only one of the choices in such questions. You may use the following values of physical constants wherever necessary. c = x 10 8 ms -1 h = 6.6 x 10-4 Js e = 1.6 x C µ o = 4π x 10-7 TmA -1 o = x C 2 N -1 m -2 1 = 9 x 10 9 Nm 2 C -2 4π o m e = 9.1 x 10-1 kg m n = x kg m p = 1.67 x kg Avogadro s number = 6.02 x 10 2 per gram mole Boltzmann constant = 1.8 x 10-2 JK -1 SECTION:A 1 Name the equivalent gate representing this circuit and draw its logic symbol. 1 2 Write nuclear reactions for + decay of 6 11 C 1 Two nuclei have their mass numbers in the ratio 1 : 8 What is the ratio of their (i) nuclear radii? (ii) nuclear density? 1 4 In a single slit diffraction experiment, the width of the slit is made double the original width. How does it affect the size and intensity of the central diffraction band? 1 5 The figure shows a plot of three curves a, b, c showing the variation of photocurrent vs collector plate potential for three different intensities I1, I2 and I having frequencies 1, 2 and respectively incident on a photosensitive surface. Page 1 of 6

2 1 6 Point out two curves for which incident radiations have same frequencies but different intensities. SECTION:B A proton and an particle have the same de-broglie wavelength. Determine the ratio of (i) their accelerating potentials (ii) their speeds. 2 7 The ratio of intensity of maxima and minima in an interference pattern is 100:64. Calculate the ratio of intensities of the coherent sources producing this pattern? 2 8 Define the term modulation index for an AM wave. What should be the modulation index for an AM wave for which maximum amplitude is a while the minimum amplitude is b? 2 9 Polarization of a beam of light by reflection is best achieved when reflected and refracted rays are at right angles to each other. Show that the polarizing angle of incidence is then given by ip = tan -1? 2 10 Draw a circuit diagram to show how a photodiode is biased. Draw its characteristic curves for two different illumination intensities. OR With the help of a diagram, show the biasing of a light emitting diode (LED). Give its two advantages over conventional incandescent lamps. 2 SECTION:C 11 A plane wave front approaches a plane surface separating two media. If the medium one is (optically) denser and medium two is (optically) rarer, construct the refracted wave front using Huygen s principle. Hence prove Snell s law. 12 (a) Given a block diagram of a generalized communication system. Identify the boxes X and Y. (b) Distinguish between Point to Point and Broadcast modes of communication. Also give one example each. 1 Figure shows energy level diagram of hydrogen atom. Page 2 of 6

3 (a) Find out the transition which results in the emission of a photon of wavelength 496nm. (b) Which transition corresponds to the emission of radiation of maximum wavelength? Justify your answer. 14 In Young's double slit experiment, the two slits are 0.0cm apart and the screen is placed at a distance of 1.5m away from the slits. The distance between the central fringe and fourth dark fringe is 1cm. Calculate the wavelength of light used. How the fringe width will be affected if the whole apparatus immersed in water of refractive index n. 15 Light of intensity I and frequency is incident on a photosensitive surface and causes photoelectric emission. What will be the effect on anode current when (i) the intensity of light is gradually increased, (ii) the frequency of incident radiation is increased and (iii) the anode potential is increased? In each case, all other factors remain the same. Explain, giving justification in each case. 16 (a) Draw a ray diagram for the formation of image by a compound microscope in normal adjustment. (b) Write expression for its resolving power and magnifying power? Mention two factors by which the resolving power of a microscope can be increased. 17 Two semiconductor materials X and Y shown in the given figure are made by doping germanium crystal with indium and arsenic respectively. The two are joined end to end and connected to a battery as shown (i) Will the junction be forward biased or reverse biased? (ii) Sketch a V-I graph for this arrangement. (iii) Draw energy level diagram of the same and compare it with that without biasing. 18 The nucleus of an atom of 92Y 25, initially at rest decays by emitting an - particle. Write the decay equation. It is given that the binding energies per nucleon of the parent and daughter nuclei are 7.8MeV and 7.85MeV respectively and that of α -particle is 7.07 MeV/nucleon. Assuming Page of 6

4 the daughter nucleus to be formed in the unexcited state neglecting its share in the energy of the reaction, calculate the energy of the emitted -particle. 19 (a) Write three characteristic features to distinguish between the interference fringes in Young s double slit experiment and the diffraction pattern obtained due to a narrow single slit. (b) A parallel beam of light of wavelength 500nm falls on a narrow slit and the resulting diffraction pattern is observed on a screen 1m away. It is observed that the first maxima is at a distance of 2.5mm away from the centre. Find the width of the slit. 20 Which mode of propagation is used by short wave broadcast services having frequency range from few MHz up 0 MHz? Explain diagrammatically how long distance communication can be achieved by this mode. Why is there an upper limit frequency of waves used in this mode? 21 (a) Good quality sun-glasses made of polaroids are preferred over ordinary colored glasses. Justify your answer (b) Two polaroids P1 and P2 are placed in crossed positions. A third Polaroid P is kept between P1 and P2 such that pass axis of P is parallel to that of P1. How would the intensity of light (I2) transmitted through P2 vary as P is rotated? Draw a plot of intensity I2 vs the angle, between pass axes of P1 and P. 22 Define the term binding energy of nucleus. Which of the two 92U 25 or 56Ba 144 has a higher value of B E per nucleon? Give the formula for BE/nucleon for a nucleus of mass number A and atomic number Z. Name the nucleus of low atomic number that is much more stable than its immediate neighbors. OR (a) The short wavelength limits of the Lyman, Paschen and Balmer series, in hydrogen spectrum are denoted by L, P and B respectively. Arrange these wavelengths in increasing order. (b) Using the graph shown in the figure for stopping potential Vs incident frequency of photons, calculate plank s constant. SECTION:D 2 When Puja, a student of 10 th class, watched her mother washing clothes in the open, she observed coloured soap bubbles and was curious to know why the soap bubbles appear coloured. In the evening when her father, an engineer by profession, came home, she asked Page 4 of 6

5 him this question. Her father explained to her the basic phenomenon of physics due to which the soap bubbles appear coloured. (a) What according to you are the values displayed by Puja and her father? (b) State the phenomenon of light involved in the formation of coloured soap bubbles. 4 SECTION:E 24 (a) Draw a schematic arrangement of Geiger-Marsden experiment showing the scattering of a-particles by a thin foil of gold. Why is it that most of the -particles go straight through the foil and only a small fraction gets scattered at large angles? Draw the trajectory of the a-particle in the coulomb field of a nucleus. What is the significance of impact parameter and what information can be obtained regarding the size of the nucleus? (b) Estimate the distance of closest approach to the nucleus (Z = 80) if a 7.7 MeV -particle before it comes momentarily to rest and reverses its direction. OR (a) Define the terms decay constant and Half-life for a radioactive sample. (b) Use the basic law of radioactive decay, to show that radioactive nuclei follow an exponential decay law. Hence obtain a formula for the half-life of a radioactive nuclide, in terms of its disintegration constant. (c) A radioactive isotope has a half-life of 5 years. How long will it take the activity to reduce to.125%? 5 25 (a) Consider two coherent sources S1 and S2 producing monochromatic waves to produce interference pattern. Let the displacement of the wave produced by S1 be given by y1 = a Cos t and displacement by S2 be y2 = a Cos( t + ). Find an expression for the amplitude of the resultant displacement at a point and show that the intensity at that point will be I = 4a 2 Cos 2 ( /2). Hence establish the conditions for constructive and destructive interference. (b) What is the effect on the interference fringes in Young s double slit experiment when (i) the width of the source slit is increased; (ii) the monochromatic source is replaced by a source of white light? OR 5 Draw a ray diagram to show the formation of the image of a distant object by an astronomical telescope in the normal adjustment position. Obtain an expression for the magnifying power of the telescope in this adjustment. A giant refracting Telescope has an objective lens of focal length 15m and an eye piece of focal length 1cm. If this telescope is used to view moon, what is the diameter of the image of the moon formed by the objective lens? The diameter of the moon is.48 x 10 6 m and distance of moon from the surface of earth is.8 x 10 8 m. Page 5 of 6

6 26 (i) The ratios of number density of free electrons to holes (ne/nh), for two different materials A and B, are equal to one and less than one respectively. Name the type of semiconductor to which A and B belong. Draw energy band diagram for A and B. (ii) The Black Box shown here, converts the input voltage wave form into output voltage waveform as is shown in the figure. Draw the circuit diagram of the circuit present in the Black Box a give a brief description of its working. OR (a) Figure shows the input waveform which is converted by a device X into an output waveform. Name the device and explain its working using the proper circuit. Derive the expression for its voltage gain and power gain. 5 (b) Draw the output characteristics of a base biased transistor in CE configuration Page 6 of 6

Mock Examination Physics 2 nd Book Time 3 Hrs MM : 70

Mock Examination Physics 2 nd Book Time 3 Hrs MM : 70 SECTION A 1. How does the angle of minimum deviation of a glass prism vary, If the incident violet light is replaced with red light? 2. What is principle