# 12th physics 2013 guess question paper

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- On 13/02/2013
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- In PHYSICS

** 12th Physics 2013 Guess Question Paper**

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**SAMPLE PAPER-2013 CLASS-XII SUBJECT- PHYSICS**

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*Time allowed: 3 hours Maximum Marks: 70*

me = 9 x 10^{-31 } kg |

**Q1.** Draw an equipotential surface for a (a) point charge (b) electric dipole.

**Q2.** If a wire is stretched to double its original length without loss of mass, how will resistivity of the wire be influenced?

**Q3.** Paramagnetic material display greater magnetization as their temperature is lowered why?

**Q4.** How a quality factor of a LCR circuit changes when a resistance is increased? Write the relation

**Q5.** Write two sources of radio waves production.

**Q6.** The polarizing angle of a medium is 60^{0}. What is the refractive index of the medium?

**Q7.** Name the device which shows the variation of current (I) with voltage (V) as shown:

**Q8.** Write two necessity of modulation in communication.

**Q9.** An electric flux of -6 x 10^{3} Nm^{2}/C passes normally through a spherical Gaussian surface of radius 10cm, due to a point charge placed at the centre. What is the charge enclosed by the Gaussian surface?

( ii ) If the radius of the surface is doubled, how much flux would pass through the surface?

**Q10.** 4 cells of identical emf E, internal resistance r, are connected in series to a variable resistor. The following graph shows the variation of terminal voltage of the combination with the current output:

(i) What is the emf of each cell used?

(ii) For what current from the cells, does maximum power dissipation occur in the circuit?

**Q11.** Define Quality factor. Why should it have a high value for receiver circuits in radio?

**Q12.** By what percentage would the range of an antenna increase if its length is increased by 21%

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**Q13.** In young’s double slit experiment, the two slits0.15 mm apart are illuminated by monochromatic light of wave length 450 nm. The screen is 1 m away from the slits.

(a) Find the distance of the second bright fringe and second dark fringe from the central maximum.

(b) How will the fringe pattern change if the screen is moved away from the slits?

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**Q14.** The half-life of a radioactive sample is 30 seconds. Calculate ( i ) the decay constant, and

( ii ) time taken for the sample to decay to 3/4th of its initial value.

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**Q15.** An electron is moving at 10^{6} m/s in a direction parallel to a current of 5 A, flowing through an infinitely long straight wire, separated by a perpendicular distance of 10cm in air. Calculate the magnitude of the force experienced by the electron. What is the direction of this force?

**Q16.** Draw a logic circuit diagram showing how a NAND gate can be converted into a NOT gate.

**Q17.** What is an zener diode? As compared to a normal diode are the following higher or lower in the zener diode? (a) Doping (b) Depletion width (c) Potential barrier.

**Q18.** A ray of light while travelling from a denser to a rarer medium undergoes total internal reflection. Derive the expression for the critical angle in terms of the speed of light in the respective medium.

**Q19.**Explain with the help of a circuit diagram, the use of potentiometer for the determination of internal resistance of a primary cell. Derive the necessary mathematical expression.

**Q20.** In the circuit shown R_{1}= 4W, R_{2}= R_{3}= 15W, R_{4}= 30W and E= 10V.Calculate the equivalent resistance of the circuit and the current in each resistor.

**Q21.** How a secondary rain bow is formed? Draw the diagram of the secondary rainbow formation through a water drop. How it is different from primary rain bow?

**Q22.** The following are the observations regarding an unknown beam “X”. What does each signify?

(a) “X” shows interference and diffraction (b) It travels in vacuum with the speed of 3x10^{8}m/s

(c) It does not get deflected on passing through an electric field

(d) After passing through a nicol prism, the intensity is reduced.

**Q23.** A bar magnet is placed in a uniform magnetic field find the expression of net force and torque .Write the expression of the work done as bar magnet rotates from angle α to β .

**Q24.**State Huygens’s postulates and verify Snell's law of refraction using wave theory.

**Q25. State **Using a Gauss theorem derive an expression for the electric field due to a charged spherical shell.

(ii)Plot a graph between Electric field intensity and distance

**Q26.** Bhavika’s grandmother has recently started having problem in reading the newspaper clearly. She took her father to a eye specialist and got a spectacles made for her.

(a) What are the values displayed by Bhavika

(b) Draw the diagram to show the eye defect and its correction using a suitable spectacle.

**Q27**. **(a) **Explain input and output characteristics of a common emitter transistor graphically. Draw the circuit diagram. (b)Two amplifiers are connected one after the other in series (cascaded).The first amplifier has a voltage gain of 10 and the second has a voltage gain of 20. If the input signal is 0.01 volt, calculate the output ac signal.

OR

How a transistor as an oscillator works. Draw its diagram and explain the role of feed back in circuits. Write two types of oscillator.

**Q28.** (a) Draw a schematic sketch of a cyclotron. Explain briefly how it works and how it is used to accelerate the charged particles. **(b)**An electron emitted by a heated cathode and accelerated through a potential difference of 2.0 kV, enters a region with uniform magnetic field of 0.15 T. Determine the trajectory of the electron if the field (i) is transverse to its initial velocity, (ii) makes an angle of 30º with the initial velocity.

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**OR**

(a)State Biot-Savart’s law. Using the law derive the expression for the magnetic field due to a current carrying circular loop at a point on the axis of the coil.

(b) At what distance from the centre on the axis of the coil will the magnetic field be 1/8^{th} of its value at the centre.

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**Q29.** In a modified Young’s double slit experiment, the source “S” is asymmetrically placed behind the slits such that the difference SS_{2} – SS_{1} = λ/2. Write the expression for

(a) Path difference at a general point “P” on the screen

(b) Condition for maxima and minima

(c) Shift in the position of the central fringe.

OR

Draw the variation of intensity with angle in single slit diffraction experiment. Derive the expression for the central fringe width .How ray optics is a limiting case of wave optics. Determine angular separation between central maximum and first order maximum of the diffraction pattern due to a single slit of width 0.25mm when light of wavelength 5890 A^{0} is incident on it normally.

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