**Guess Paper – 2008**

**Class – XII**

**Subject – Physics**

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**CLASS-XII SUB-PHYSICS MAX MARKS-60**

**DATE- TIME-3hrs.**

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__GENERAL INSTRUCTIONS.__

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**1. ****All** **questions are compulsory.**

**2. ****There is no overall choice. How ever, an internal choice has been given provided in one question of 2 marks, one question of 3 marks, and three questions of five marks.**

**3. ****Question numbers 1-8 are very short answer type questions, carrying 1 mark each.**

**4. ****Question numbers 9-18 are short answer type questions, carrying 2 marks each.**

**5. ****Question numbers 19-27 are short answer type questions, carrying 3 marks each.**

**6. ****Question numbers 28-30 are long answer type questions, carrying 5 marks each.**

**7. ****Calculators are not allowed. However you may use log tables if necessary.**

C = 3 x 10 ^{8 }m/s

h = 6.6 x 10^{ –34} Js

e = 1.6 x 10 ^{–19} C

μ_{0} = 4 x 10 ^{–7} TmA^{ –1}

1. Consider the situation of the two poles P and Q shown in the figure below. What are the signs of P and Q?

p

Q_{}

2. The polarizing angle of a medium is 60^{0}. What is the refractive index of the medium?

3. Name 2 materials, which are used for making standard resistance coils.

4. Lorentz force is given by F = I (LxB). Of these, name the pairs of vectors which are always at right angles to each other.

- What is the power factor of an LCR circuit at resonance?

6. An inductor of 10mH carries a current of 2A. The current is increased to 5A in 10 seconds. What is the voltage induced in the inductor?

7. Compare the radii of two nuclei with mass number 1 and 27 respectively.

8. Define Attenuation.

9. A charge of 5C is placed at the origin and –10C is placed at the point x = 30. Find a point on the x axis at which (a) Electric field is zero (b) Potential is zero.

10. What are electric field lines? Mention 2 properties.

11. Name the elements of earth’s magnetism.

- How can one distinguish between on unpolarised light beam and a linearly polarized light beam using a Polaroid?
- The photoelectric cut-off voltage in a certain experiment is 1.5 V. What is the maximum K.E. of photoelectrons emitted?
- Explain the effect of potential on photoelectric current and draw the graph for different intensities.
- Obtain the binding energy (in MeV) of a nitrogen nucleus (
^{14}_{7}N ), given mass of N = 14.00307 u. - The input of a 2-input NAND gate is fed to a Not gate, write down the truth table for the combination for all possible inputs of A and B.

17. A communication system mainly consists of three major parts. Name them. Draw the block diagram of a generalized communication system.

- A transmitting antenna at the top of a tower has a height 32 m and the height of the receiving antenna is 50 m.What is the maximum distance between them for satisfactory communication in LOS mode? Given radius of the earth is 6.4 x 10
^{6}m. - The electrostatic force on a small sphere of charge 4C due to another small sphere of charge 8C in air is F. What is the distance b/w the 2 spheres. What is the force on the –8C sphere due to the first sphere. What will the force be if the spheres are dipped in a liquid having dielectric constant K.
- Deduce the condition for balance in a Wheatstone bridge. Using the principle of Wheatstone Bridge, describe the method to determine the specific resistance of a wire in the laboratory. Draw the circuit diagram and write the formula used.

21. A resistance has color coding as ( green, red, brown,) and other one has (blue, black, grey).

Find the ratio of power dissipated in first to the power dissipated in second if both are separately connected across 220V-power supply.

- Draw the ray diagram showing the formation of image of an object using a compound microscope?
- A converging lens has a focal length of 200m in air it is made of a material of refractive index 1.6 If it is immersed in a liquid of refractive index 1.3 what will be its new focal length?

24. When an inductor L and a resistance R in series are connected across a 12 V , 50Hz ac source, a current of 0.5A flows in the circuit. The current differs in phase from applied voltage by π/3 radian. Calculate the value of R.

25. Briefly explain the construction and working of a transformer. Mention 3 factors responsible for the decrease in efficiency.

26.With a schematic arrangement of the Geiger-Marsden experiment, explain α-particle scattering.

27. Write short notes on

(1) Microwaves

(2) X-Rays

28. What is Hysterisis? Draw the hysterisis loops for soft iron and steel. Explain Retentivity and Coercivity. Hence explain which material you would prefer for making

1) Permanent magnet

2) Core of a transformer

3) Electromagnet

**Or**

Explain the construction and working of a moving coil galvanometer. A moving coil galvanometer is made of a coil of radius 10cm and has 1000 turns. The strong horse shoe magnets create a magnetic field of 0.2T and the spring has a spring constant of 0.5 N/m. Find the

1) Galvanometer constant G

2) Current sensitivity I_{s}

3) Voltage Sensitivity V_{s}

Explain how a galvanometer can be made more sensitive?

29. Define principle of superposition. Drive the expression for the fringe width in young’s double slit interference experiment? Write two conditions for interference. What is the difference between interference pattern and diffraction pattern?

**Or**

** **State the postulates of Huygens wave theory. Prove laws of reflection and refraction using Huygens wave theory.

**30**. Draw a labelled diagram of transistor oscillator. Briefly explain its principle and state how the oscillation is sustained?

**Or **

Draw the energy band diagrams of p –type and n- type semi-conductors. Explain with a circuit diagram the working of a full wave rectifier